Method and for the detection of biological molecules using a two particle complex

ABSTRACT

Methods, compositions and kits for detecting analytes of interest in a sample using electrogenerated chemiluminescence are provided. Compositions comprising at least one solid support that entraps or contains an electrogenerated chemiluminescent moiety also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.11/159,412, filed on Jun. 23, 2005, which claims the benefit of U.S.Provisional Patent Application 60/581,719, filed on Jun. 23, 2004; theentire contents of which are hereby incorporated by reference, for anyand all purposes.

BACKGROUND

There is a continuous and expanding need for rapid, highly specificmethods of detecting and quantifying analytes such as chemical,biochemical, and biological substances. In particular, methods formeasuring small quantities of pharmaceuticals, metabolites, biologicalmarkers, microorganisms, viruses and other pathogens are desired. Thepresence of these materials can often be determined by binding methodswhich exploit the high degree of specificity which characterizes manybiological systems. Known methods which rely on binding to detect amolecule of interest present in a sample include nucleic acidhybridization techniques and protein-ligand interactions such asantibody-antigen binding. In these methods, the existence of a complexof diagnostic value is typically indicated by the presence/activation orabsence/deactivation of an observable label which has been attached toone or more of the materials comprising the complex.

Sensitivity and selectivity are both desirable attributes of any systemfor detecting specific molecules of interest present in a samplecomprised of a plurality of components. Sensitivity, in DNAhybridization and other bioassays for the detection of biologicalmolecules of interest, is important in clinical diagnostics (Liron andFisher Eds. Novel Approaches in Biosensors and Rapid Diagnostic Assays,Kluwer Academic/Plenum Publishers: New York, 2000; Kenton et al. 1992,Clin. Chem. 38:873; Chistodoulides et al. 2002, Anal. Chem. 74:3030),forensic chemistry (Heller, 2002, Annu Rev. Biomed. Eng. 4:129; Nelsonet al. 1996, J. Forensic Sci. 41:557), environmental investigations(Lucarelli et al. 2002, Talanta 56:949; Min et al. 2002, Anal. Biochem.303:186), pharmaceutical studies (Heller, 2002, Annu Rev. Biomed. Eng.4:129; Pollice et a1.1985, Clin. Lab. Med. 5:463), and biologicalwarfare agent detection (Smith, 2002, Anal. Chem. 74:462 A; Miao andBard, 2003, Anal. Chem. 75:5825). Thus any system which provides forsensitive and selective detection of molecules of interest will havebroad applicability in all of these fields.

Electrochemiluminescence (ECL) methods have been widely used in bindingstudies, because of their high sensitivity, wide dynamic range, andselectivity (U.S. Pat. No. 6,316,607; Bard, A. J. Ed. ElectrogeneratedChemiluminescence, Marcel Dekker New York, 2004). For example, a varietyof techniques are available for the detection of DNA, whereelectrochemical, fluorescent, and ECL active labels attached to a targetsingle stranded DNA (t-ssDNA) produce the measurable signal in theanalysis process (Liron and Fisher Eds. Novel Approaches in Biosensorsand Rapid Diagnostic Assays, Kluwer Academic/Plenum Publishers: NewYork, 2000; Yang and Ngo Eds. Biosensors and Their Applications, KluwerAcademic/Plenum Publishers: New York, 2000; Cunningham, Introduction toBioanalytical Sensors, J. Wiley & Sons, Inc.: New York, 1998). Thesensitivity of these methods is often limited since the intensity of themeasured signal is generally proportional to the amount of t-ssDNA, andtraditionally, only one or a few labels can be attached to one t-ssDNA.A number of approaches have been developed in which one DNA can belabeled with a larger number of labels, so that a higher sensitivity canbe achieved (Wang and Merkoci, 2003, Langmuir 19:989; Zhao et al. 2003,J. Am. Chem. Soc. 125:11474). These methods do not provide thesensitivity required to detect quantities in the femtomole (fmol) range.Nor do they provide low non-specific binding, the ability to distinguishbetween complementary hybridization and a 2 base pair mismatch ormultiple measurements.

The need remains, therefore, for highly sensitive detection systems(e.g., in the fmol range) that provide high selectivity and lownon-specific binding. The system should have broad applicability so thatit can be used to detect virtually any molecule of interest, provided itis capable of binding to or interacting with at least one other molecule(e.g., a specific binding partner). When the molecule of interest is anucleic acid, e.g., DNA, the system should be able to distinguishbetween each of the following: complementary hybridization, at least2-base pair-mismatched hybridization, and non-complementary DNAhybridization.

Ideally, the detection system will provide both a simple treatment toeliminate non-specific binding of the ECL label and high stability ofthe ECL label thereby allowing for the possibility of taking multiplemeasurements, without a loss of signal. Each of these needs, at least,is met by certain embodiments of those disclosed herein.

SUMMARY

The present application relates generally to methods and compositionsfor detecting analytes of interest in a sample. An analyte of interestcan be associated with a disease or condition afflicting humans or otherliving organisms. Analytes of interest include toxins, chemical orbiological warfare agents, and environmental pollutants. In certainembodiments the compositions may comprise a first and second carrier, ananalyte of interest contained within a sample, an electrogeneratedchemiluminescent (ECL) moiety entrapped or contained throughout thefirst carrier and at least one specific binding partner of the analyteof interest linked to at least one of the first and second carrier.Certain embodiments relate to methods of using these compositions todetect an analyte of interest in a sample.

In certain embodiments, methods and compositions for detecting ananalyte of interest in a sample that is rapid, sensitive, and selectiveare provided. The application thus relates to methods and compositionsfor accurately detecting (e.g., with low occurrence of false positivesignals) small quantities (e.g., 1 fmol) of analytes of interest thatare contained within a sample. This desired sensitivity is achieved, atleast in part, by providing a plurality of ECL molecules entrapped orcontained within a first carrier.

In certain embodiments, the application provides a method of detectingan analyte of interest in a sample comprising: (a) forming a compositioncomprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a first carrier containing A        and B is either linked to the analyte of interest or linked to a        first specific binding partner of the analyte of interest; C is        the sample which may contain the analyte of interest; and D is a        second carrier which is either linked to the analyte of interest        or linked to a second specific binding partner of the analyte of        interest; wherein k, u, and x are each an integer equal to or        greater than 1; (b) separating a complex comprising A, B, D, and        the analyte of interest from other components of the        composition; (c) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by exposing the moiety to        electrochemical energy; and (d) detecting the emitted        electromagnetic radiation and thereby detecting the presence of        the analyte of interest, provided that B and D are not both        linked to the analyte of interest.

In certain embodiments, the application provides a method of detecting abiological molecule of interest in a sample, comprising: (a) forming acomposition comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a first solid support        encasing or containing A and B is either linked to the        biological molecule of interest or linked to a first specific        binding partner of the biological molecule of interest; C is the        sample which may contain the biological molecule of interest;        and D is a second solid support which is either linked to the        biological molecule of interest or linked to a second specific        binding partner of the biological molecule of interest; wherein        k, u, and x are each an integer equal to or greater than 1; (b)        separating a complex comprising A, B, D, and the biological        molecule of interest from other components of the        composition; (c) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by directly exposing the moiety to        electrochemical energy; and (d) detecting the emitted        electromagnetic radiation and thereby determining the presence        of the biological molecule provided that B and D are not both        linked to the biological molecule of interest.

In some embodiments, the biological molecule of interest can be aprotein. In some embodiments, the biological molecule of interest can bea nucleic acid.

In certain embodiments, the application provides a composition usefulfor the detection of an analyte of interest in a sample, comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a first carrier containing A        and B is either linked to the analyte of interest or linked to a        first specific binding partner of the analyte of interest; C is        the sample which may contain the analyte of interest; and D is a        second carrier which is either linked to the analyte of interest        or linked to a second specific binding partner of the analyte of        interest; wherein k, u, and x are each an integer equal to or        greater than 1, provided that B and D are not both linked to the        analyte of interest.

In certain embodiments, the application provides a composition usefulfor the detection of a biological molecule in a sample, comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a first solid support        containing A and B is either linked to the biological molecule        of interest or linked to a specific binding partner of the        biological molecule of interest; C is the sample which may        contain the biological molecule; and D is a second solid support        which can be directly linked to the biological molecule of        interest or linked to a second specific binding partner of the        biological molecule of interest; wherein k, u, and x are each an        integer equal to or greater than 1, provided that B and D are        not both linked to the biological molecule of interest.

In some embodiments, the biological molecule of interest can be aprotein. In some embodiments, the biological molecule of interest can bea nucleic acid.

In certain embodiments, the application provides a method of detecting anucleic acid molecule of interest in a sample, comprising: (a) forming acomposition comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a bead that is soluble in an        organic solvent, for example, a polystyrene bead, containing A        and B is either linked to the nucleic acid molecule of interest        or linked to a first specific binding partner of the nucleic        acid molecule of interest; C is the sample which may contain the        nucleic acid molecule of interest; and D is a magnetic bead        which is linked to the nucleic acid molecule of interest or        linked to a second specific binding partner of the nucleic acid        molecule of interest; wherein k, u, and x are each an integer        equal to or greater than 1; (b) separating a complex comprising        A, B, D, and the nucleic acid molecule of interest from other        components of the composition; (c) dissolving B in an organic        solvent; (d) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by directly exposing the moiety to        electrochemical energy; and (e) detecting the emitted        electromagnetic radiation and thereby detecting the presence of        the nucleic acid molecule of interest, provided that B and D are        not both linked to the nucleic acid molecule of interest.

In certain embodiments, the nucleic acid molecule of interest is adeoxyribonucleic acid (DNA). In some embodiments, the nucleic acidmolecule of interest is a ribonucleic acid (RNA).

In certain embodiments, the application provides a composition usefulfor detecting a nucleic acid molecule of interest in a samplecomprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is a Ru(bpy)₃[B(C₆F₅)₄]₂ moiety, which can be induced        to repeatedly emit electromagnetic radiation by direct exposure        to an electrochemical energy source; B is a polystyrene bead        containing A and B is either linked to the nucleic acid molecule        of interest or linked to a binding partner of the nucleic acid        molecule of interest; C is the sample which may contain the        nucleic acid molecule of interest; and D is a magnetic bead        which is either linked to the nucleic acid molecule of interest        or linked to a specific binding partner of the nucleic acid        molecule of interest; wherein k, u, and x are each an integer        equal to or greater than 1, provided that B and D are not both        linked to the nucleic acid molecule of interest.

In certain embodiments, the application provides a composition fordetecting a nucleic acid molecule of interest in a sample comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is either linked to the nucleic acid molecule        of interest or linked to a first specific binding partner of the        nucleic acid molecule of interest; C is the sample which may        contain the nucleic acid molecule of interest; and D is a        magnetic bead which is linked to the nucleic acid molecule of        interest or linked to a second specific binding partner of the        nucleic acid molecule of interest; wherein k, u, and x are each        an integer equal to or greater than 1, provided that B and D are        not both linked to the nucleic acid molecule of interest.

In certain embodiments, the application provides a method of detecting aprotein of interest in a sample, comprising: (a) forming a compositioncomprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is linked either to the protein of interest        or to a first specific binding partner which specifically binds        to the protein of interest; C is the sample which may contain        the protein of interest; D is a magnetic bead which can be        linked to the protein of interest or to a second specific        binding partner which specifically binds to the protein of        interest; wherein k, u, and x are each an integer equal to or        greater than 1; (b) separating a complex comprising A, B, D, and        the protein molecule of interest from other components of the        composition; (c) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by directly exposing the moiety to        electrochemical energy; and (d) detecting the emitted        electromagnetic radiation and thereby detecting the presence of        the protein of interest, provided that B and D are not both        linked to the protein of interest.

In certain embodiments, the first and/or the second binding partner ofthe protein of interest can be an antibody or a specific bindingprotein.

In certain embodiments, the application provides a composition fordetecting a protein of interest in a sample comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is either linked to the protein of interest        or linked to a first specific binding partner of the protein of        interest; C is the sample which may contain the protein molecule        of interest; and D is a magnetizable bead which is either linked        to the protein of interest or linked to a second specific        binding partner which specifically binds to the protein molecule        of interest; and wherein k, u, and x are each an integer equal        to or greater than 1, provided that B and D are not both linked        to the protein of interest.

In certain embodiments, the first and/or the second binding partner ofthe protein molecule of interest can be an antibody or a specificbinding protein.

The application also provides methods for performing competitive bindingassays to detect an analyte of interest. In certain embodiments, theapplication provides a method of detecting an analyte of interest in asample, comprising: (a) forming a composition comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a first carrier containing A        and B is either linked to an analog of the analyte of interest        or linked to a specific binding partner of the analyte of        interest; C is the sample which may contain the analyte of        interest; and D is a second carrier which is either linked to an        analog of the analyte of interest or linked to a specific        binding partner of the analyte of interest; wherein k, u, and x        are each an integer equal to or greater than 1; (b) separating a        complex comprising A, B, D from other components of the        composition; (c) inducing the ECL moiety in the complex to        repeatedly emit electromagnetic radiation by directly exposing        the moiety to electrochemical energy; and (d) detecting the        emitted electromagnetic radiation and thereby detecting the        presence of the analyte of interest, provided that only one of B        and D is linked to the analog of the analyte of interest; and        further provided that if B is linked to the analog of the        analyte of interest, then D is linked to a binding partner of        the analyte of interest and if B is linked to a binding partner        of the analyte of interest, then D is linked to the analog of        the analyte of interest.

In related embodiments, the application provides a method of detecting anucleic acid molecule of interest in a sample comprising: (a) forming acomposition comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is either linked to an analog of the nucleic        acid of interest or linked to a specific binding partner of the        nucleic acid molecule of interest; C is the sample which may        contain the nucleic acid molecule of interest; and D is a        magnetic bead which is either linked to an analog of the nucleic        acid of interest or linked to a specific binding partner of the        nucleic acid molecule of interest; wherein k, u, and x are each        an integer equal to or greater than 1; (b) separating a complex        comprising A, B, D, and the nucleic acid molecule of interest        from other components of the composition; (c) dissolving B in an        organic solvent; (d) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by directly exposing the moiety to        electrochemical energy; and (e) detecting the emitted        electromagnetic radiation and thereby detecting the presence of        the nucleic acid molecule of interest, provided that only one of        B and D is linked to the analog of the nucleic acid of interest;        and further provided that if B is linked to the analog of the        nucleic acid molecule of interest, then D is linked to a binding        partner of the nucleic acid molecule of interest and if B is        linked to a binding partner of the nucleic acid molecule of        interest, then D is linked to the analog of the nucleic acid        molecule of interest.

In some embodiments, the application provides, a method of detecting aprotein of interest in a sample, comprising: (a) forming a compositioncomprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is linked either to an analog of the protein        of interest or to a specific binding partner which specifically        binds to the protein of interest; C is the sample which may        contain the protein of interest; D is a magnetic bead which is        either linked to an analog of the protein of interest or to a        specific binding partner which specifically binds to the protein        of interest; wherein k, u, and x are each an integer equal to or        greater than 1; (b) separating a complex comprising A, B, D, and        the protein of interest from other components of the        composition; (c) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by directly exposing the moiety to        electrochemical energy; and (d) detecting the emitted        electromagnetic radiation and thereby detecting the presence of        the protein of interest; provided that only one of B and D is        linked to the analog of the protein of interest; and further        provided that if B is linked to the analog of the protein of        interest, then D is linked to a specific binding partner of the        protein of interest and if B is linked to a specific binding        partner of the protein of interest, then D is linked to the        analog of the protein of interest.

In some embodiments, the application provides compositions forperforming competitive binding assays for the detection of analytes ofinterest. In some embodiments, the application provides a compositionfor detecting an analyte of interest in a sample comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a first carrier containing A        and B is either linked to an analog of the analyte of interest        or linked to a first specific binding partner of the analyte of        interest; C is the sample which may contain the analyte of        interest; D is a second carrier which can be linked to the        analog of the analyte of interest or linked to a second specific        binding partner of the analyte of interest; and wherein k, u,        and x are each an integer equal to or greater than 1, provided        that only one of B and D is linked to the analog of the analyte        of interest and further provided that if B is linked to the        analog of the analyte of interest, then D is linked to the        specific binding partner of the protein of interest and if B is        linked to the specific binding partner of the protein of        interest, then D is linked to the analog of the protein of        interest.

In certain embodiments of the composition the analyte of interest is anucleic acid. In some embodiments of the composition, the analyte ofinterest is a protein.

In a related embodiment, the application provides a composition fordetecting a nucleic acid molecule of interest in a sample comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is either linked to an analog of the nucleic        acid molecule of interest or linked to a specific binding        partner of the nucleic acid molecule of interest; C is the        sample which may contain the nucleic acid molecule of interest;        D is a magnetic bead which is either linked to the analog of the        nucleic acid molecule of interest or linked to the specific        binding partner of the nucleic acid molecule of interest; and        wherein k, u, and x are each an integer equal to or greater than        1, provided that only one of B and D is linked to the analog of        the nucleic acid molecule of interest and further provided that        if B is linked to the analog of the nucleic acid molecule of        interest, then D is linked to the binding partner of the nucleic        acid molecule of interest and if B is linked to the binding        partner of the nucleic acid molecule of interest, then D is        linked to the analog of the nucleic acid molecule of interest.

In certain embodiments, the nucleic acid molecule of interest is adeoxyribonucleic acid (DNA). In certain embodiments the nucleic acidmolecule of interest is a ribonucleic acid (RNA).

In some embodiments, the application provides a composition fordetecting a protein of interest in a sample comprising:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein A is an ECL moiety which can be induced to repeatedly        emit electromagnetic radiation by direct exposure to an        electrochemical energy source; B is a polystyrene bead        containing A and B is either linked to an analog of the protein        of interest or linked to a specific binding partner of the        protein of interest; C is the sample which may contain the        protein of interest; D is a magnetic bead which is either linked        to the analog of the protein of interest or linked to the        specific binding partner of the protein of interest; and wherein        k, u, and x are each an integer equal to or greater than 1,        provided that only one of B and D is linked to the analog of the        protein of interest and further provided that if B is linked to        the analog of the protein of interest, then D is linked to the        binding partner of the protein of interest and if B is linked to        the binding partner of the protein of interest, then D is linked        to the analog of the protein of interest.

Additional embodiments provide kits useful for performing certainmethods and forming certain compositions disclosed herein. In someembodiments, the application provides a kit for detecting an analyte ofinterest in a sample, comprising an ECL moiety which can be induced torepeatedly emit electromagnetic radiation by direct exposure to anelectrochemical energy source; a first carrier containing the ECLmoiety, wherein the first carrier is either linked to an analog of theanalyte of interest or linked to a first specific binding partner of theanalyte of interest; and a second carrier which is either linked to theanalog of the analyte of interest or linked to a second specific bindingpartner of the analyte of interest.

A skilled artisan would understand that any of the embodiments,including methods, compositions and kits, described above, can alsoinclude more than one ECL moiety, provided each of the ECL moietiesemits light at different wavelengths. Compositions, methods, and kitscomprising two or more ECL moieties can be used, for example, to detectmore than one analyte in a sample.

A skilled artisan would understand that any of the embodiments,including methods, compositions and kits, described above, can alsoinclude more than one ECL moiety, provided each of the ECL moieties emitlight at different wavelengths. More than one ECL moiety is useful, forexample, when more than one analyte can be detected.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the methods and compositions, as describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a certain embodiment where theanalyte of interest is a DNA molecule linked to a polystyrene bead whichalso serves as a first carrier containing an ECL label. Also shown is asecond bead, which is magnetic and serves as a second carrier linked toa DNA molecule which is complementary to the DNA molecule linked to thepolystyrene bead. The two DNA molecules bind to form a complex.Application of a magnetic field to the complex provides a means ofisolating the analyte of interest (e.g., DNA) and detection of the ECLlabel provides a means of detection of the analyte of interest.

FIG. 2 shows fluorescent images of carboxylate polystyrene beads havinga 10 μm diameter. FIG. 2( a) shows the beads after entrapping ofRu(bpy)₃[B(C₆F₅)₄]₂, and FIG. 2( b) shows the beads after covalentbinding of avidin onto the surface of Ru(bpy)₃[B(C₆F₅)₄]₂ loaded beads.The exposure times used were 30 seconds. The specimens were excited atlamda_(ex) 490 nm.

FIG. 3 is a scanning electron micrograph (SEM) image obtained after DNAhybridization between the probe DNA-magnetic bead conjugate (DNA-MB) andthe complementary DNA conjugated to an avidin coated polystyrene beadcontaining Ru(bpy)₃[B(C₆F₅)₄]₂ (represented as DNA-Ru(II)<PSB/Avidin).The concentration used for both DNA molecules was 5 μM, and the size ofthe PSB and the MB was 10 μm and 1.0 μm, respectively.

FIG. 4 shows (a) cyclic voltammetric (CV) and (b) ECL responses obtainedfrom 0.10 μM Ru(bpy)₃[B(C₆F₅)₄]₂ in acetonitrile (MeCN) containing 0.10M (TBA)BF₄ electrolyte-0.10 M tripropylamine (TPrA) coreactant at a 2.2mm diameter Pt electrode with a scan rate of 50 mV/s. For comparison, CVof 1.0 mM Ru(bpy)₃[B(C₆F₅)₄]₂ in MeCN containing 0.10 M (TBA) BF₄ in theabsence of TPrA is presented in (c). The experimental conditions in (c)were as in (a) and (b), but the CV current was multiplied by 10.

FIG. 5 shows (a) TPrA and (b) TPrA-trifluoroacetic acid (TFAA)concentration effect on ECL intensity. All samples contained 0.10 μMRu(bpy)₃[B(C₆F₅)₄]₂ and 0.10 M (TBA)BF₄ in MeCN. The working electrodewas a Pt electrode having a 2.2 mm diameter. The scan rate was 50 mV/s.

FIG. 6 shows the elimination of ECL background for the TPrA-MeCN system.In (a) 0.10 M TPrA and 0.10 M (TBA) BF₄-MeCN was used. In (b), the sameconditions as in (a) were used with the addition of 0.055 M TFM. In (c)the same conditions as in (b) were used with the addition of 1.0% (v/v)H₂O. In (d) 0.10 M (TBA) BF₄-MeCN was used. FIG. 6( e) shows therelative ECL intensities depicted in (a)-(d).

FIG. 7 shows the ECL intensity as a function of Ru(bpy)₃[B(C₆F₅)₄]₂concentration (a) and the number of 10 μm diameter polystyrene beadsloaded with Ru(bpy)₃[B(C₆F₅)₄]₂ (b).

FIG. 8 shows the ECL detection of DNA hybridization. FIG. 8( a) showsthat the DNA hybridization between probe DNA-MB (1.0 μm) and targetDNA—Ru(II)<PSB/Avidin (10 μm) occurred at a ratio of MB/PSB=29. FIG. 8(b) shows that the DNA hybridization occurred between probe DNA-MB (2.8μm) and target DNA—Ru(II)<PSB/Avidin (10 μm) at a ratio of MB/PSB=4.

FIG. 9 shows a Poisson distribution test using (a) 2.8 μm and (b) 1.0 μmdiameter streptavidin coated MB reacted with 10 μm diameter biotinylatedPSB. The “Bound PSB %” was calculated from the number of PSB found inthe supernatant after the magnetic separation of MB-PSB conjugates fromthe reaction media.

FIG. 10 shows the binding capacities of (a) 10 μm diameter streptavidincoated polystyrene beads entrapped with Ru(bpy)₃ ²⁺, (b) 1.0 μm diameterstreptavidin coated magnetic beads, and (c) 2.8 μm diameterstreptavidin-coated magnetic beads for a biotinylated 23-mer-ss DNA(p-ssDNA) obtained from fluorescein biotin titration experiments.

FIG. 11 shows the molecular structures of DPA (a) and RUB (b).

FIG. 12 is flow chart depicting the steps in a procedure for loadingaromatic hydrocarbons into polystyrene beads.

FIG. 13 shows fluorescent images of (a) DPA loaded PSB; (b) RUB loadedPSB; and (c) PSB only.

FIG. 14 shows the CV and ECL behavior of (a) DPA loaded PSB dissolved inMeCN and (b) 0.25 mM DPA acetonitrile solution using TPrA as acoreactant.

FIG. 15 shows the CV and ECL behavior of (a) RUB loaded PSB dissolved inMeCN and (b) 35 μM RUB acetonitrile solution using TPrA as a coreactant.

FIG. 16 shows the relationship between ECL signal and concentration of Creactive protein (CRP).

DESCRIPTION OF THE EMBODIMENTS A. Definitions

The term “antibody”, as used herein, means an immunoglobulin or a partthereof, and encompasses any polypeptide comprising an antigen-bindingsite regardless of the source, method of production, or othercharacteristics. The term includes for example, polyclonal, monoclonal,monospecific, polyspecific, humanized, single-chain, chimeric,synthetic, recombinant, hybrid, mutated, and CDR-grafted antibodies. Apart of an antibody can include any fragment which can bind antigen, forexample, an Fab, F(ab)₂, Fv, scFv.

The term “analyte of interest”, as used herein, means any molecule, oraggregate of molecules, including a cell or a cellular component of avirus, found in a sample. Also included are fragments of any moleculefound in a sample. An analyte of interest can be an organic compound, anorganometallic compound or an inorganic compound. An analyte of interestcan be a nucleic acid (e.g., DNA, RNA, a plasmid, a vector, or anoligonucleotide), a protein (e.g., an antibody, an antigen, a receptor,a receptor ligand, or a peptide), a lipoprotein, a glycoprotein, a ribo-or deoxyribonucleoprotein, a peptide, a polysaccharide, alipopolysaccharide, a lipid, a fatty acid, a vitamin, an amino acid, apharmaceutical compound (e.g., tranquilizers, barbiturates, opiates,alcohols, tricyclic antidepressants, benzodiazepines, anti-virals,anti-fungals antibiotics, steroids, cardiac glycosides, or a metaboliteof any of the preceding), a hormone, a growth factor, an enzyme, acoenzyme, an apoenzyme, haptens, lechtins, a substrate, a cellularmetabolite, a cellular component or organelle (e.g., a membrane, a cellwall, a ribosome, a chromosome, a mitochondria, or a cytoskeletoncomponent). Also included in the definition are toxins, pesticide,herbicides, and environmental pollutants. The definition furtherincludes complexes comprising one or more of any of the examples setforth within this definition.

The term “analog of the analyte of interest”, as used herein, means asubstance that competes with the analyte of interest for binding to aspecific binding partner. An analog of the analyte of interest can be aknown amount of the analyte of interest itself that is added to competefor binding to a specific binding partner with analyte of interestpresent in a sample.

The term “carrier”, as used herein, means one or more solid or liquidencapsulating substances. A carrier can comprise organic or inorganiccompounds and it can be used for at least one of the following: topresent a sample, to present a specific binding partner, or to containor entrap an ECL moiety. Carriers are described in further detail infra.

The terms “containing” or “contained”, as used herein, refer to thenon-specific association between the interior of a carrier and an ECLmoiety, such that the ECL moiety and the carrier are in physical contactwith one another, but are not necessarily attached to each other. Incertain embodiments, an ECL moiety contained within a carrier can belinked to the carrier. In certain embodiments the ECL moiety containedwithin a carrier is not linked to the carrier. The termscontaining/contained are used interchangeably with the terms“encased/encasing,” and “entrapped/entrapping.”

The term “hybridizing”, as used herein, refers to the formation ofduplexes between one nucleotide sequence and a second nucleotidesequence under appropriate conditions. In some embodiments theappropriate conditions can be stringent conditions. Stringent conditionsare sequence-dependent and will be different in different circumstances.Longer sequences hybridize specifically at higher temperatures (see,e.g., Sambrook et al. 1989, Molecular Cloning A Laboratory Manual, ColdSpring Harbor Laboratory, N.Y. and Ausubel et al. 1989, CurrentProtocols in Molecular Biology, Greene Publishing Associates and WileyInterscience, N.Y.). Generally, stringent conditions are selected to beabout 5° C., lower than the thermal melting point (T_(m)) for thespecific sequence at a defined ionic strength and pH. The T_(m) is thetemperature (under defined ionic strength, pH, and nucleic acidconcentration) at which 50% of the polynucleotides complementary to thetarget sequence hybridize to the target sequence at equilibrium.Typically, stringent conditions will be those in which the saltconcentration is less than about 1.0 M sodium ion, typically about 0.05to 1.0 M sodium ion concentration (or other salts) at pH 7.0 to 8.3 andthe temperature is at least about 30° C. for short probes (e.g., 10 to50 nucleotides) and at least about 60° C. for long probes (e.g., greaterthan 50 nucleotides). Stringent conditions can also be achieved with theaddition of destabilizing agents such as formamide. Each increase of 1%in the formamide concentration of a solution lowers the T_(m) of a DNAduplex by about 0.7° C.

Hybridization can occur between polynucleotides that are 100%complementary, i.e., when there are no mismatches between the twostrands of a double-stranded nucleic acid. Hybridization can also occurwhen there are mismatches between the two strands of a double-strandednucleic acid. Complementary hybridization, as used herein, refers to thehybridization between two strands of nucleic acid where there is no morethan one mismatch between the two hybridized strands of adouble-stranded nucleic acid.

The term “linked” as used herein encompasses both direct covalentconnections between two moieties, direct noncovalent connections betweentwo moieties, and indirect connections between two moieties that aremediated by one or more additional moieties. For example, a directcovalent connection between two moieties can include an amide bondbetween two amino acids, a direct noncovalent connections between twomoieties can include an ionic interaction between a metal and a base toform a salt, or a hydrogen bond between two water molecules. Indirectconnections between two moieties that are mediated by one or moreadditional moieties can include a fusion protein, such as an Ig fusionprotein and a receptor, such as a TNF receptor, where the bond betweenthe Ig and the TNF receptor is mediated by a linker, such as short aminoacid sequence that is not native to either the Ig or TNF receptor.

The term “linked” does not encompass connections that are mediated by ananalyte of interest.

The term “magnetizable” as used herein refers to a property of matterwherein the permeability of the matter differs from that of free space.The term includes paramagnetizable and superparamagnetizable.

The term “nucleic acid,” as used herein, refers to polymers comprised ofdeoxyribonucleotides or ribonucleotides in either single- ordouble-stranded form. Typically a single-stranded nucleic acid willcomprise more than 100 bases and a double-stranded nucleic acid willcomprise more than 100 base pairs. The term “nucleic acid” encompassesnucleic acids containing naturally occurring nucleotides as well asanalogues of natural nucleotides that have binding properties similar tothe reference nucleic acid. The term nucleic acid also includes cDNA oran mRNA encoded by a gene. A nucleic acid will be able to hybridize toits complement through complementary base pairing, e.g., via a hydrogenbond.

The term “oligonucleotide,” as used herein, refers to a single-strandednucleic acid that typically is less than or equal to 100 bases long. Ofcourse, complementary oligonucleotides can be annealed to form adouble-stranded polynucleotide. As used herein, an oligonucleotide caninclude natural (i.e., A, G, C, T, or U) or modified bases. In addition,the bases in an oligonucleotide can be joined by a linkage other than aphosphodiester bond, so long as it does not interfere with interstrandbase pairing. Thus, for example, oligonucleotides can be peptide-nucleicacids in which the constituent bases are joined by peptide bonds ratherthan phosphodiester linkages. (see e.g. Nielson, 2001, Current Opinionin Biotechnology 12:16). It will be understood by one of skill in theart that oligonucleotides can hybridize with sequences lacking completecomplementarity with the probe sequence and the methods described hereincan be used to distinguish between binding that is completelycomplementary and that which is less than completely complementary.Optionally, the oligonucleotides can be directly labeled withradioisotopes, chromophores, lumiphores, chromogens, or ECL moieties orcan be indirectly labeled, for example, with biotin to which astreptavidin or avidin complex can later bind.

The term “polynucleotide,” as used herein, refers to a polymer comprisedof more than 2 nucleotides, and less than 100 nucleotides.

The term “sample,” as used herein, means any specimen derived from, ororiginating in, a biological system. Biological systems includeecological systems (e.g., a water, air or soil specimen) or, organisms(e.g., a plant, an animal, fungi, bacteria, other eukaryotes orprokaryotes), or viruses or prions. The sample can contain an analyte ofinterest. The term sample can also include an isolated, e.g., purifiedanalyte of interest.

The term “specific binding partner,” as used herein, refers to a firstmolecule that can form a relatively stable complex with a secondmolecule under physiologic conditions. In general, specific binding ischaracterized by a relatively high affinity and a relatively low tomoderate capacity. Nonspecific binding usually has a low affinity with amoderate to high capacity. Typically, binding is considered specificwhen the affinity constant K_(a) is higher than about 10⁶ M⁻¹, or ishigher than about 10⁸ M⁻¹. A higher affinity constant indicates greateraffinity, and thus greater specificity. Antibodies typically bindantigens with an affinity constant in the range of 10⁶ M⁻¹ to 10⁹ M⁻¹ orhigher. If desired, nonspecific binding can be reduced withoutsubstantially affecting specific binding by varying the bindingconditions. Such conditions are known in the art, and a skilled artisanusing routine techniques can select appropriate conditions. Theconditions can be defined, for example, in terms of molecularconcentration, ionic strength of the solution, temperature, time allowedfor binding, concentration of unrelated molecules (e.g., serum albumin,milk casein), etc.

Examples of specific binding partners include complementary nucleic acidsequences (e.g., two DNA sequences which hybridize to each other; twoRNA sequences which hybridize to each other; or a DNA and an RNAsequence which hybridize to each other), an antibody and an antigen, areceptor and a ligand (e.g., TNF and TNFr-I, CD142 and Factor Vila, B7-2and CD28, HIV-1 and CD4, ATR/TEM8 or CMG and the protective antigenmoiety of anthrax toxin), an enzyme and a substrate, or a molecule and abinding protein (e.g., vitamin B12 and intrinsic factor, folate andfolate binding protein). A specific binding partner can also be ananalog of a naturally occurring specific binding partner. Examples ofanalogs include azidothymidine (AZT), an analog of a nucleotide whichbinds to HIV reverse transcriptase, puromycin, an analog of the terminalaminoacyl-adenosine part of aminoacyl-tRNA, and methotrexate, an analogof tetrahydrofolate. Other analogs can be derivatives of the analyte ofinterest.

B. Electro Generated Chemiluminescent Substances

In certain embodiments, the application provides for detecting ananalyte of interest in a sample using ECL. The ECL moiety can be anycompound that can be induced to repeatedly emit electromagneticradiation by direct exposure to an electrochemical energy source. Insome embodiments, the ECL moiety can be induced to repeatedly emitelectromagnetic radiation in the presence of a coreactant. In someembodiments, the ECL moiety can comprise a metal-containing organiccompound wherein the metal is chosen, for example, from ruthenium,osmium, rhenium, iridium, rhodium, platinum, palladium, molybdenum, andtechnetium. In some embodiments, the metal is ruthenium or osmium. Themetal can also be chosen, for example, from rare earth metals, includingbut not limited to cerium, dysprosium, erbium, europium, gadolinium,holmium, lanthanum, lutetium, neodymium, praseodymium, promethium,terbium, thulium, and ytterbium. In some embodiments, the metal iscerium, europium, terbium, or ytterbium.

According to certain embodiments, a metal-containing ECL moiety asemployed herein may have the formula BF₄

M(P)_(m)(L¹)_(n)(L²)_(o)(L³)_(p)(L⁴)_(q)(L⁵)_(r)(L⁶)_(s)

wherein M is a metal; P is a polydentate ligand of M; L¹, L², L³, L⁴, L⁵and L⁶ are ligands of M, each of which can be the same as, or differentfrom, each other ligand; m is an integer equal to or greater than 1;each of n, o, p, q, rand s is an integer equal to or greater than zero;and P, L¹, L², L³, L⁴, L⁵ and L⁶ are of such composition and number thatthe ECL moiety can be induced to emit electromagnetic radiation and thetotal number of bonds to M provided by the ligands of M equals thecoordination number of M.

In some embodiments, M is ruthenium. In some embodiments, M is osmium.

In certain embodiments, the ECL moiety has one polydentate ligand of M.In some embodiments, the ECL moiety has more than one polydentateligand. In embodiments comprising more than one polydentate ligand of M,the polydentate ligands can be the same or different. Polydentateligands include aromatic and aliphatic ligands. Suitable aromaticpolydentate ligands include aromatic heterocyclic ligands and can benitrogen-containing, such as, for example, bipyridyl, bipyrazyl,terpyridyl, 1,10 phenanthroline, and porphyrins.

Suitable polydentate ligands can be unsubstituted, or substituted by anyof a large number of substituents known to the art. Suitablesubstituents include for example, alkyl, substituted alkyl, aryl,substituted aryl, aralkyl, substituted aralkyl, carboxylate,carboxaldehyde, carboxamide, cyano, amino, hydroxy, imino,hydroxycarbonyl, aminocarbonyl, amidine, guanidinium, ureide, maleimidesulfur-containing groups, phosphorus containing groups, and thecarboxylate ester of N-hydroxysuccinimide.

Additionally, at least one of L¹, L², L³, L⁴, L⁵ and L⁶ can be apolydentate aromatic heterocyclic ligand. Furthermore, at least one ofthese polydentate aromatic heterocyclic ligands can contain nitrogen.Suitable polydentate ligands include, but are not limited to, bipyridyl,bipyrazyl, terpyridyl, 1,10 phenanthroline, a porphyrin, substitutedbipyridyl, substituted bipyrazyl, substituted terpyridyl, substituted1,10 phenanthroline or a substituted porphyrin. These substitutedpolydentate ligands can be substituted with an alkyl, substituted alkyl,aryl, substituted aryl, aralkyl, substituted aralkyl, carboxylate,carboxaldehyde, carboxamide, cyano, amino, hydroxy, imino,hydroxycarbonyl, aminoarbonyl, amidine, guanidinium, ureide, maleimide asulfur-containing group, a phosphorus-containing group or thecarboxylate ester of N-hydroxysuccinimide.

In some embodiments, the ECL moiety can contain two bidentate ligands,each of which can be bipyridyl, bipyrazyl, terpyridyl, 1,10phenanthroline, substituted bipyridyl, substituted bipyrazyl,substituted terpyridyl or substituted 1,10 phenanthroline.

In certain embodiments, the ECL moiety can contain three bidentateligands, each of which can be bipyridyl, bipyrazyl, terpyridyl, 1,10phenanthroline, substituted bipyridyl, substituted bipyrazyl,substituted terpyridyl or substituted 1,10 phenanthroline. The ECLmoiety can comprise ruthenium. In some embodiments, the ECL moiety cancomprise ruthenium, two bidentate bipyridyl ligands, and one substitutedbidentate bipyridyl ligand.

In some embodiments, the ECL moiety can contain a tetradentate ligandsuch as a porphyrin or substituted porphyrin.

The ECL moiety can have one or more monodentate ligands, a wide varietyof which are known to the art. Suitable monodentate ligands include, forexample, carbon monoxide, cyanides, isocyanides, halides, and aliphatic,aromatic and heterocyclic phosphines, amines, stibines, and arsines.

Certain embodiments of this ECL moiety comprisebis(2,2′-bipyridyl)ruthenium(II) and tris(2,2′-bipyridyl)ruthenium(II).

One or more of the ligands of M may be attached to additional chemicallabels, such as, for example, radioactive isotopes, fluorescentcomponents, or additional luminescent ruthenium- or osmium-containingcenters.

In some embodiments, the ECL moiety is tris(2,2′-bipyridyl)ruthenium(II)tetrakis(pentafluorophenyl)borate. In some embodiments, the ECL moietyisbis[(4,4′-carbomethoxy)-2,2′-bipyridine]2-[3-(4-methyl-2,2′-bipyridine-4-yl)propyl]-1,3-dioxolaneruthenium (II). In some embodiments, the ECL moiety isbis(2,2′bipyridine)[4-(butan-1-al)-4′-methyl-2,2′-bipyridine]ruthenium(II). In a further embodiment, the ECL moiety isbis(2,2′-bipyridine)[4-(4′-methyl-2,2′-bipyridine-4′-yl)-butyricacid]ruthenium (II). In some embodiments, the ECL moiety is(2,2′-bipyridine)[cis-bis(1,2-diphenylphosphino)ethylenel]{2-[3-(4-met-hyl-2,2′-bipyridine-4′-yl)propyl]-1,3-dioxolane}osmium(II). In yet a further embodiment, the ECL moiety isbis(2,2′-bipyridine)[4-(4′-methyl-2,2′-bipyridine)-butylamine]ruthenium(II). In some embodiments, the ECL moiety isbis(2,2′-bipyridine)[1-bromo-4(4′-methyl-2,2′-bipyridine-4-yl)butane]ruth-enium(II). In still a further embodiment, the ECL moiety isbis(2,2′-bipyridine)maleimidohexanoic acid,4-methyl-2,2′-bipyridine-4′-butylamide ruthenium (II).

In some embodiments, the ECL moiety does not comprise a metal and canbe, for example, rubrene or 9,10-diphenylanthracene.

In some embodiments, the ECL moiety can be contained or encased in acarrier. The number of ECL molecules encased in or adsorbed to thecarrier will depend on the size of the ECL molecule and the size of thecarrier. The carrier can contain 1×10²-1×10²⁰, 1×10²-1×10¹⁵,1×10⁴-1×10¹², 1×10²-1×10¹⁰, 1×10⁶-1×10¹⁰, or 1×10⁶-1×10⁹ ECL molecules.In some embodiments, the ECL moiety can be contained or encased in acarrier and linked to the surface of the carrier, e.g., by a covalentbond or a non-covalent interaction.

The term “ECL coreactant,” as used herein, herein, pertains to achemical compound that either by itself or via its electrochemicalreduction oxidation product(s), plays a role in the ECL reactionsequence.

Often ECL coreactants can permit the use of simpler means for generatingECL (e.g., the use of only half of the double-step oxidation-reductioncycle) and/or improved ECL intensity. In some embodiments, coreactantscan be chemical compounds which, upon electrochemicaloxidation/reduction, yield, either directly or upon further reaction,strong oxidizing or reducing species in solution. A coreactant can beperoxodisulfate (i.e., S₂O₈ ², persulfate) which is irreversiblyelectro-reduced to form oxidizing SO₄ ⁻ ions. The coreactant can also beoxalate (i.e., C₂O₄ ²⁻) which is irreversibly electro-oxidized to formreducing CO₂ ⁻ ions. A class of coreactants that can act as reducingagents is amines or compounds containing amine groups, including, forexample, tri-n-propylamine (i.e., N(CH₂CH₂CH₃)₃, TPrA). In someembodiments, tertiary amines can be better coreactants than secondaryamines. In some embodiments, secondary amines can be better coreactantsthan primary amines.

Coreactants include, but are not limited to, lincomycin;clindamycin-2-phosphate; erythromycin; 1-methylpyrrolidone; diphenidol;atropine; trazodone; hydroflumethiazide; hydrochlorothiazide;clindamycin; tetracycline; streptomycin; gentamicin; reserpine;trimethylamine; tri-n-butylphosphine; piperidine; N,N-dimethylaniline;pheniramine; bromopheniramine; chloropheniramine; diphenylhydramine;2-dimethylaminopyridine; pyrilamine; 2-benzylaminopyridine; leucine;valine; glutamic acid; phenylalanine; alanine; arginine; histidine;cysteine; tryptophan; tyrosine; hydroxyproline; asparagine; methionine;threonine; serine; cyclothiazide; trichlormethiazide;1,3-diaminopropane; piperazine, chlorothiazide; hydrazinothalazine;barbituric acid; persulfate; penicillin; 1-piperidinyl ethanol;1,4-diaminobutane; 1,5-diaminopentane; 1,6-diaminohexane;ethylenediamine; benzenesulfonamide; tetramethylsulfone; ethylamine;di-ethylamine; tri-ethylamine; tri-iso-propylamine; di-n-propylamine;di-iso-propylamine; di-n-butylamine; tri-n-butylamine;tri-iso-butylamine; bi-iso-butylamine; s-butylamine; t-butylamine;di-n-pentylamine; tri-n-pentylamine; n-hexylamine; hydrazine sulfate;glucose; n-methylacetamide; phosphonoacetic acid; and/or salts thereof.

Coreactants also include, but are not limited to, N-ethylmorpholine;sparteine; tri-n-butylamine; piperazine-1,4-bis(2-ethanesulfonic acid)(PIPES); triethanolamine; dihydronicotinamide adenine dinucleotide;1,4-diazobicyclo(2.2.2)octane; ethylenediamine tetraacetic acid; oxalicacid; 1-ethylpiperidine; di-n-propylamine;N,N,N′,N′-Tetrapropyl-1,3-diaminopropane; DAB-AM-4, Polypropyleniminetetraamine Dendrimer; DAB-AM-8, Polypropylenimine octaamine Dendrimer;DAB-AM-16, Polypropylenimine hexadecaamine Dendrimer; DAB-AM-32,Polypropylenimine dotriacontaamine Dendrimer; DAB-AM-64,Polypropylenimine tetrahexacontaamine Dendrimer;3-(N-Morpholino)propanesulfonic acid;3-Morpholino-2-hydroxypropanesulfonic acid; Glycyl-glycine;2-Morpholinoethanesulfonic acid;2,2-Bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol;N-(2-Acetamido)iminodiacetic acid; N,N-Bis(2-hydroxyethyl)taurine;N-(2-Hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid);N,N-Bis(2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid;4-(N-Morpholino)butanesulfonic acid;4-(2-Hydroxyethyl)piperazine-1-(2-hydroxypropanesulfonic acid) Hydrate;piperazine-1,4-bis(2-hydroxypropanesulfonic acid)dihydrate;4-(2-Hydroxyethyl)piperazine-1-propanesulfonic acid;N,N-Bis(2-hydroxyethyl)glycine;N-(2-Hydroxyethyl)piperazine-N′-(4-butanesulfonic acid); and/or saltsthereof.

ECL measurements according to the present methods can be made in organicsolvents such as acetonitrile, in partially aqueous systems, or inaqueous systems. A suitable electrode for the electrochemical reductionof an ECL moiety can be, for example, a Pt electrode or an electrodecomprised of an alloy of Pt and Ir.

C. Carriers

In certain embodiments, the application provides for a first and secondcarrier which can be used in the detection of an analyte of interest.The first and second carriers can serve at least one of severalfunctions, including presentation of a sample, presentation of aspecific binding partner, containment or entrapment of an ECL moiety,and providing a means for separating a complex formed between an analyteof interest and a specific binding partner from other components of thecomposition.

Either the first or second carrier can comprise an ECL moiety. Incertain embodiments, the ECL moiety can be contained in the carrier.Because the ECL moiety is contained within a carrier, the applicationprovides for readily releasing the ECL moiety from the carrier, e.g., bychanging certain conditions such as the nature of the solvent. Incertain embodiments, e.g., where the carrier is a solid supportcomprised of a material such as plastic, the ECL moiety is not blendedinto the carrier. In some embodiments, the ECL moiety can be covalentlylinked to the surface of the carrier and contained within the carrier.In some embodiments, the ECL moiety can be contained within the carrierand adsorbed to the surface of the carrier. The first carrier canoptionally be comprised of the sample containing the analyte ofinterest. In certain embodiments, the sample can be linked to thesurface of the first carrier, thus making it available for binding witha specific binding partner. In certain embodiments, however, the samplecan be linked to neither the first or second carrier. In thisembodiment, the sample can be in solution.

In certain embodiments, either the first carrier or second carrier cancomprise a specific binding partner of the analyte of interest. Thespecific binding partner can be linked to the surface of the firstcarrier thereby making it accessible for binding to the analyte ofinterest.

In embodiments comprising a second carrier, the second carrier cancomprise a specific binding partner of the analyte of interest. Thespecific binding partner can be linked to the surface of the secondcarrier thereby making it accessible for binding to the analyte ofinterest. The second carrier can comprise a means for separating acomplex formed between the analyte of interest and the specific bindingpartner. In certain embodiments, the second carrier can provide a meansof separating the complex formed between the analyte of interest and thespecific binding partner from other components of the composition. Forexample, the second carrier can be magnetizable allowing the complexformed between the analyte of interest and the specific binding partnerto be separated from other components of the composition using a magnet.In certain embodiments, the magnet used to separate the complex fromother components of the composition can be located proximal to anelectrode that can be used to introduce electrochemical energy into thesystem as described, for example, in U.S. Pat. Nos. 5,935,779 and6,325,973.

In certain embodiments, at least one of the first and second carrierscan be a solid support. In some embodiments both the first and secondcarriers are solid supports. The solid support can comprise a particle,i.e., a polymer having a length greater than 1000 micrometers in atleast one dimension, a nanoparticle, i.e., a polymer having a length inthe range of 1-1000 nanometers in at least one dimension, or amicroparticle, i.e., a polymer having a length greater than 1000nanometers, but less than or equal to 1000 micrometers in at least onedimension. In certain embodiments the solid support can have a threedimensional shape including both irregular and regular shapes, e.g.spherical, cubic, conical.

The solid supports can comprise a bead, a gel, or a membrane. A membranecan comprise, for example, nitrocellulose, nylon, polyvinylidenefluoride (PVDF) or carboxylated polyvinylidene (U.S. Pat. No.6,037,124). The membrane can be coated with polyvinyl benzyl dimethylhydroxyethyl ammonium chloride, polyvinyl benzyl benzoyl aminoethyldimethyl ammonium chloride, polyvinyl benzyl tributyl ammonium chloride,copolymers of polyvinyl benzyl trihexyl ammonium chloride and polyvinylbenzyl tributyl ammonium chloride, copolymers of polyvinyl benzyl benzyldimethyl ammonium chloride and polyvinyl aminoethyl dimethyl ammoniumchloride and copolymers of polyvinyl benzyl phenyl ureidoethyl dimethylammonium chloride and polyvinyl benzyl benzyl dimethyl ammonium chloride(U.S. Pat. No. 5,336,596). The solid support can comprise any materialwhich can be linked to a specific binding partner of the analyte ofinterest and/or the sample (e.g. polystyrene, sepharose, sephadex)and/or which can contain or entrap an ECL moiety. Solid supports cancomprise any synthetic organic polymer such as polyacrylic, vinylpolymers, acrylate, polymethacrylate, polyacrylamide, polyacylonitriles,and polyolefins. Solid supports can also comprise a carbohydratepolymer, e.g., agarose, cellulose, hyaluronic acid, chitin, acyl gellan,dextran, carboxymethylcellulose, carboxymethyl starch, carboxymethylchitin, poly(lactide-co-ethylene glycol). Solid supports can compriseinorganic oxides, such as silica, zirconia, e.g., carbon clad zirconia(U.S. Pat. No. 5,182,016), titania, ceria, alumina, manganese, magnesia(i.e., magnesium oxide), calcium oxide, controlled pore glass (CPG).Solid supports can also comprise combinations of some of theabove-mentioned supports including, but not limited to,dextran-acrylamide. A solid support can be prepared to minimizenon-specific interactions with the specific binding partner and/or theanalyte of interest.

In certain embodiments where at least one of the first or secondcarriers is a solid support, the solid support can be insoluble in anaqueous environment, but soluble in an organic environment, e.g.,acetonitrile, ether, chloroform, benzene. For embodiments in which anECL moiety is entrapped or otherwise associated with such a solidsupport, the ECL moiety can be released by placing the solid support inan organic environment, thereby facilitating detection of the ECLmoiety. An organic environment can include a solvent that is 70-100%,80-100%, 90-99%, 99-99.99% organic solvent (volume/volume).

In some embodiments, at least one of the first or second carriers is agel having a melting point in the range of 30° C.-60° C., e.g., lowmelting temperature agarose. In these embodiments, heating the complexabove the melting point of the carrier containing the ECL moiety willrelease the ECL moiety and thereby facilitate detection.

In certain embodiments, the solid support is a bead, e.g., a polystyrenebead. In embodiments where both the first and second carriers are beads,the first carrier can have an ECL moiety contained or entrapped withinit, and the second carrier can be a magnetizable bead. Both theECL-containing bead and the magnetizable bead can have a diameter in therange of 0.1 μm-100 μm, 0.5 μm-50 μm, 1 μm-20 μm, or 0.5 μm-10 μm. Insome embodiments, the first carrier can have a diameter of 10 μm and thesecond carrier can have a diameter of 1 μm. In some embodiments, thefirst carrier can have a diameter of 10 μm and the second carrier canhave a diameter of 2.8 μm.

In certain embodiments, at least one of the carriers can comprise aliquid. The liquid can comprise at least one amphiphilic molecule. Anamphiphilic molecule is one having both polar and non-polar portions andwhich can form aggregates, e.g. micelles, in an aqueous environment.Thus a micelle can be comprised of any fatty acid ion such as palmitateor oleate. A micelle can comprise one or more non-ionic detergents,e.g., Triton X-100, or Octyl-.beta.-D-glucoside. A micelle can compriseone or more ionic detergents, e.g., sodium dodecyl sulfate,deoxycholate, lysolecithin. In some embodiments, a micelle can compriseboth ionic and nonionic detergents.

Thus in certain embodiments, at least one of the first and secondcarriers can be a micelle. The micelle can be linked to the sample, sothat the analyte of interest is exposed on the surface of the micelle,thus allowing the specific binding partner to contact the analyte ofinterest. The ECL moiety can be contained within the interior of themicelle. Disruption of the micelle, e.g. through agitation orsonication, or oxidation or reduction, will thus provide a means ofreleasing the ECL and facilitate detection of the analyte of interest.

In certain embodiments, the carrier can be a liposome. Liposomes aremicroscopic spherical vesicles that form when phospholipids arehydrated. When mixed in water under low shear conditions, thephospholipids arrange themselves in sheets, the molecules aligning sideby side in like orientation, “heads” up and “tails” down. These sheetsthen join tails-to-tails to form a bilayer membrane in a phospholipidsphere with an aqueous center. Liposomes can be of uniform size, e.g.,200 nm in diameter. Liposomes enable water soluble and water insolublematerials to be used together in a formulation without the use ofsurfactants or other emulsifiers. Water soluble materials are dissolvedin the water in which the phospholipids are hydrated, and when theliposomes form these materials are trapped in the aqueous center. Theliposome wall, being a phospholipid membrane, holds fat solublematerials such as oils. Liposomes can be comprised of stabilized naturalphospholipid mixtures, synthetic identical-chain phospholipids,glycolipid-containing liposomes, bipolar fatty acids, methylmethylenex-linked, lipoprotein-coated, or carbohydrate-coated. The sample can bepresented on the surface of the liposome to facilitate binding of thespecific binding partner or the sample. The liposome can contain withinit (i.e., in the aqueous center or in the surrounding lipid) an ECLmoiety, see, e.g., U.S. Pat. No. 6,706,861.

D. Methods of Linking a Sample or Specific Binding Partner to a Carrier

The sample containing the analyte of interest or the specific bindingpartner can be linked to a carrier by any means known in the art. Forexample, crosslinking reagents can be used for proteins and nucleicacids (Lund et al. 1988, Nucleic Acids Res. 16:10861). Similarly,photoreactive crosslinking reagents have been used for both nucleicacids and proteins (Penchovsky et al. 2000, Nucleic Acids Res.28(22):98; Harrison et al. 1989, Biochemistry 28:6023). Selection of theappropriate means will depend on the nature of the sample and the natureof the carrier. The linkage can be, for example, by a covalent bond, anon-covalent interaction such as an electrostatic interaction, ahydrophobic interaction, a hydrophilic interaction, a van der Waalsinteraction, or a hydrogen bond. Selecting a method of linking a sampleto a carrier is well within the ordinary skill in the art.

In certain embodiments, ligands are immobilized or “linked” directly toa carrier by forming covalent chemical bonds between particularfunctional groups on the ligand (e.g., primary amines, sulfhydryls,carboxylic acids, aldehydes) and reactive groups on the carrier.

Other linking approaches are also possible, including but not limited tousing biotin with avidin or streptavidin as a linker. Methods of usingbiotin/avidin streptavidin as linkers are known in the art (see, Wilchekand Bayer, Eds. Methods in Enzymology vol. 184, Academic Press, SanDiego 1990). In certain embodiments, N-hydroxysuccinimide (NHS) can beused to form an NHS ester of biotin. The biotin residue can be linked toa variety of functional groups including but not limited to primaryamines on lysine residues, carboxyl moieties on glutamate or aspartateresidues, or sulfhydryl moieties on cysteine residues. Avidin can becovalently linked to a carrier via an amino group on lysine afteractivation of the carrier with cyanogen bromide (CNBr).

In certain embodiments, the sample or the binding partner can be simplyadsorbed on the surface of the carrier. For example, antibodies can beadsorbed to the surface of polystyrene microspheres. For maximum surfacecoverage (up to a monolayer) in embodiments in which it is desired toadsorb a protein to the surface of a carrier, the pH of the solution canbe adjusted to, or slightly more basic than, the protein's isoelectricpoint. Using a dilute microsphere suspension (about 1% solids) ensurescoating of single microspheres. While a final protein concentration ofabout 0.1 mg/ml is usually enough to achieve a monolayer of protein,adding about 3 to about 10 times that amount ensures favorablestoichiometry and a good driving force for binding.

The surface of a carrier can be modified to facilitate the covalentlinkage of the sample or the specific binding partner. Surface-modifiedpolymeric microspheres are often made by copolymerizing styrene with asmall amount (less than about 5%) of a functional monomer, such asacrylic acid, which yields microspheres covered with —COOH groups. Othermonomers can be used to prepare microspheres with different surfacechemistries, see, e.g., U.S. Pat. No. 5,599,889.

Native silanol groups on the surface of silica microspheres can bereacted with aqueous or solvent-based silane linking agents to yieldpreactivated silica microspheres with a large variety of surfacefunctional groups. Examples include chloromethyl, carboxyl, and aminogroups. DNA and RNA can be adsorbed onto silica in the presence ofchaotropic agents. Oligonucleotides can be covalently bound tosurface-modified silica via the 5′-amino end. Lipids can be bound viathe carboxyl group on the fatty acid chain and propylamine surfacegroups on the silica as described by Boom et al., 1990, J. Clin.Microbiol., 28:495).

An analyte of interest or a specific binding partner can be incorporatedinto a micelle, see, e.g., Savic et al., 2003, Science 300:615;Maysinger et al., 2001, Biochim. Biophys. Acta. 1539(3):205.Solubilization and reconstitution of a protein into detergent micellescan be performed, for example, by slowly diluting the protein solutionin 6 M guanidine hydrochloride (Gdn.HCl) into an excess of refoldingbuffer (e.g., 3% dihexanoyl phosphatidylcholine 20 mM Tris.HCl/5 mMEDTA/0.6 M L-arginine, pH 8.5). After removing the residual Gdn-HCl, forexample, by dialysis, the solution can be concentrated by a variety oftechniques, including ultrafiltration. See, e.g., Fernandez et al. 2001,Proc. Natl. Acad. Sci. USA 98:2358.

An analyte of interest, or a specific binding partner can beincorporated into a liposome. Many methods of incorporating proteinsinto liposomes are known (see, e.g., Rigaud., et al., “Liposomes asTools for the Reconstitution of Biological Systems,” p. 71-88, inLiposomes as Tools in Basic Research and Industry, ed. Philippot, J. R.and Schuber, CRC Press, Boca Raton, Fla. (1995)). As an example,mechanical means, such as a sonicator or French press, can be used toproduce unilamellar vesicles by swelling and drying phospholipids filmsin excess buffer (Lelkes et al., 1985, J. Biol. Chem. 260:1796).Alternatively, proteins can be spontaneously incorporated into preformedliposomes catalyzed by low cholate or lysolecithin concentrations(Wrigglesworth et al., 1987, Biochem J. 246(3):737). Proteins can alsobe co-solubilized in the presence of phospholipids and detergent, toform micelles followed by the subsequent removal of the detergent. Largeliposomes can be prepared by reverse-phase evaporation and treated withvarious amounts of the detergents such as Triton X-100, octyl glucoside,or sodium cholate. At each step of the solubilization process, proteincan be added. The protein-phospholipid detergent mixtures can then besubjected to SM2 Bio-Beads treatments to remove the detergent (Rigaud etal., 1988, Biochemistry 27(8):2677). Membrane proteins can beincorporated into liposomes by providing the membrane protein insolution; providing a solution of preformed liposomes; and incubatingthe mixture. Prior to the step of providing a solution of preformedliposomes, the liposomes are formed by combining a mixture ofphospholipids with a solution of at least one type of unsaturated fattyacid (U.S. Pat. No. 6,706,861). The skilled artisan will recognize thatthere are many additional ways to link the sample to a carrier.

E. Methods of Loading an ECL Moiety into a Carrier

In certain embodiments, the ECL moiety can be linked to the surface of acarrier. Methods described above regarding linking a sample to a carriercan be similarly used to link an ECL moiety to a carrier. Where thecarrier is a solid support, e.g., a bead, the ECL moiety can be linkedto the surface of the carrier, for example, via a covalent bond, anon-covalent interaction, an electrostatic interaction, a hydrophobicinteraction, a hydrophilic interaction, a van der Waals interaction, ora hydrogen bond.

In some embodiments, the ECL moiety is soluble in organic solvents, butinsoluble in aqueous solvents. The ECL moiety can be dissolved in anorganic solvent and then mixed with a plurality of carrier particles,e.g., a bead comprised of a hydrophobic material such as polystyrene.The organic solvent containing the ECL moiety penetrates the pores ofthe carrier and, upon evaporation of the organic solvent, the ECL moietybecomes trapped or encased in the interior of the carrier. When the beadis solvated in an aqueous solvent, most or all of the ECL moiety remainsencased within the carrier. In certain embodiments, the carrier is apolystyrene bead. In some embodiments, the ECL moiety can beincorporated into a gel by forming the gel in a solution comprising theECL moiety. In some embodiments, the ECL moiety can be incorporated intoa micelle by forming the micelle in a solution comprising the ECLmoiety. In some embodiments, the ECL moiety can be incorporated into aliposome by forming the liposome in a solution comprising the ECLmoiety.

In some embodiments, the ECL moiety can be trapped inside a carrierwithout substantial loss into the surrounding media. Loss of ECL moietyto the surrounding liquid phase may be unwanted during preparation anduse. The carrier's ability to trap the ECL moiety can be fundamentallydescribed by an important physical constant termed a partitioncoefficient. The partition coefficient is K=C carrier/C liquid, where Ccarrier is the concentration of the moiety imbibed with the carrier andC liquid is the concentration of moiety not imbibed.

With a system of two phases (carrier and liquid), a moiety with apartition coefficient greater then one shows a preference to the carrierphase. High values of partition coefficient indicate a strong preferencefor the carrier phase. Conversely, a moiety with a partition coefficientless then one would prefer the liquid phase. A low partition coefficientsystem which initially had high levels of ECL moieties within thecarrier would lose moieties to the surrounding liquid phase.

In some embodiments, the partition coefficient between the carrier andan aqueous solvent is greater than about 2. In some embodiments, thepartition coefficient between the carrier and an aqueous solvent isgreater than about 10. In some embodiments, the partition coefficientbetween the carrier and an aqueous solvent is greater than about 100.There are several chemical and physical designs to achieve a highpartition coefficient. (1) The moiety can be held to the carrier bycoulombic attraction. In such case, the ECL moiety can have a netpositive charge and the carrier has a net negative charge. (2) In someembodiments, the solubility of the ECL moiety can be much greater in thecarrier phase. For example, the ECL moiety is not soluble in water andis soluble in a lypophilic polystyrene carrier. (3) In some embodiments,the ECL moiety can be trapped within the carrier because the microscopicporosity of the carrier is smaller then the moiety diameter. (4) In someembodiments, the moiety can be bounded to the carrier though covalentbonds.

F. Methods of Detecting an Analyte of Interest

The application provides various methods of detecting an analyte ofinterest contained within a sample. In some embodiments, the analyte ofinterest can be linked to a carrier, e.g., a first carrier. The analyteof interest can be present on the surface of the carrier thusfacilitating its access to a specific binding partner. In someembodiments, the analyte of interest can not be linked to any carrier.In some embodiments, the analyte of interest can be present in solution.

The methods described herein provide for at least one specific bindingpartner capable of binding specifically to the analyte of interest. Insome embodiments, the at least one specific binding partner can belinked to a carrier. In this embodiment the sample can be linked to asecond carrier.

In some embodiments, at least one specific binding partner can be abinding protein capable of specifically binding to the molecule ofinterest. The binding partner can be linked to a carrier. In thisembodiment the sample can be linked to a second carrier.

In some embodiments, at least one specific binding partner can be anoligonucleotide or a nucleic acid capable of specifically binding to theanalyte of interest. The binding partner can be linked to a carrier. Inthis embodiment the sample can be linked to a second carrier.

In some embodiments, the application provides for two specific bindingpartners, i.e., a first and a second specific binding partner, both ofwhich specifically bind to the analyte of interest. The two specificbinding partners can both be linked to a carrier. Thus, in certainembodiments, a first specific binding partner can be linked to a firstcarrier and a second specific binding partner can be linked to a secondcarrier. In this embodiment, the sample can not be linked to anycarrier. It is also contemplated that the same specific binding partnercan be linked to both the first and second carrier. In some embodiments,a polyclonal antibody which specifically binds the analyte of interestcould be linked to both the first and second carrier. In someembodiments, the analyte of interest could contain multiple copies of anepitope recognized by a monoclonal antibody or, where the analyte is anucleic acid, it could contain multiple repeats of a sequence recognizedby a probe linked to both the first and second carrier. In certainembodiments, at least one of the specific binding partners can be anantibody. It is also contemplated that both specific binding partnerscan be antibodies. The application also encompasses embodiments in whichone specific binding partner can be an antibody and a second specificbinding partner can be a specific binding protein.

In some embodiments, at least one specific binding partner can be anoligonucleotide that hybridizes with the molecule of interest in thesample. As with antibodies, it is contemplated that both specificbinding partners can be oligonucleotides or other nucleic acids thathybridize with the molecule of interest in the sample.

ECL moieties can be detected by methods well known in the art including,for example, emission and absorption spectroscopy, e.g., ultravioletabsorption, infrared absorption, and fluorescence emissions; atomicabsorption, electrochemical, e.g. anodic stripping voltametry; neutronactivation and chemical methods. In certain embodimentsphotoluminescence, chemiluminescence and electrochemiluminescencemethods are used. In some embodiments, the presence of the chemicalmoiety can be determined by inducing the ECL moiety to emitelectromagnetic radiation and detecting the emitted radiation. In someembodiments, the ECL moiety can be induced to emit electromagneticradiation by exposing the reagent mixture to electromagnetic, chemicalor electrochemical energy. In some embodiments, the ECL moiety can beinduced to emit electromagnetic radiation by exposing the reagentmixture to chemical or electrochemical energy. In certain embodiments, aco-reactant is added to aid in detecting the ECL moiety, e.g., TPrA.

Ru(bpy)₃ ²⁺ can be determined at very low concentrations usingluminescence techniques. Using the oxidative reduction method, it ispossible to detect Ru(bpy)₃ ²⁺ at concentrations of 5×10⁻⁸ M. Sodiumoxalate (1 mM) in phosphate buffer pH 5.0, can be used with a potentialpulsed at 0 to +1.4 volts versus a saturated calomel reference electrodefor 5 to 10 second intervals. Using 18 mM Na₂S₂O₈ and 0.1 Mtetra-n-butyl ammonium tetrafluoroborate in CH₃CN: H₂O (1:1 v/v),Ru(bpy)₃ ²⁺ concentrations as low as 10⁻¹³ M can be detected (see, e.g.,U.S. Pat. Nos. 6,140,138; 5,731,089; 5,714,089).

The present application also provides methods for employing ECL moietiesin assays for detecting an analyte of interest comprising: (a) forming acomplex having the formula:

-   -   (A)_(k), (B)_(u), (C), (D)_(x)        wherein, in certain embodiments, A is an ECL moiety which can be        induced to repeatedly emit electromagnetic radiation by direct        exposure to an electrochemical energy source; B is a first        carrier (linked to a specific binding partner of the analyte of        interest) which is associated with A; C is a sample which may        contain the analyte of interest, B being linked to the analyte        of interest via the binding partner of the analyte of interest;        and D is a second carrier which can be directly linked to the        analyte of interest or linked to the analyte of interest via a        second specific binding partner of the analyte of interest; k,        u, and x are each an integer equal to or greater than 1; (b)        separating the complex formed in (a) from other components of        the composition; (c) inducing the ECL moiety to repeatedly emit        electromagnetic radiation by directly exposing the moiety to        electrochemical energy; and (d) detecting the emitted        electromagnetic radiation and thereby determining the presence        of the analyte of interest.

In certain embodiments, the present method can be a competitive bindingassay, e.g., a competitive inhibition assay (see, e.g. Janeway et al.Immunobiology, Garland Publishing, New York 2001). In some embodimentsof this assay, a known quantity of the analyte of interest or an analogof the analyte of interest can be linked (the term “linked” comprisesboth covalent and noncovalent linkages) to a carrier that does notcomprise an ECL moiety, for example, a magnetic bead. A binding partnerfor the analyte of interest can be linked to a second carrier, forexample, a polystyrene bead, which does comprise an ECL moiety. In theabsence of added analyte of interest, a complex will form between theanalyte of interest linked to the first carrier and the binding partnerfor the analyte of interest linked to the second carrier, effectivelylinking the first carrier to the second carrier. The amount of ECLmoiety associated with this complex can be measured by techniques knownin the art. The presence of the analyte of interest in a sample can thenbe detected by its ability to decrease the amount of complex formed bycompetition with the carrier-linked molecule of interest for binding tothe second-carrier-linked binding partner. In certain embodiments, theamount of the analyte of interest in a sample can be quantified bycomparison with standard curves using samples comprising known amountsof the molecule of interest.

In some embodiments, the application provides a sandwich-type bindingassay for detecting an analyte of interest. In some embodiments of thisassay, a first binding partner of the analyte of interest can be linkedto a first carrier, for example a magnetic bead. A second bindingpartner of the analyte of interest can be linked to a second carrier,for example a polystyrene bead, which can comprise an ECL moiety. In thepresence of a sample containing the analyte of interest, complexescomprising both the first carrier and the second carrier can form. Theamount of ECL moiety associated with this complex, which is proportionalto the amount of the biological material of interest in the sample, canbe measured by techniques known in the art. In certain embodiments, theamount of the analyte of interest in a sample can be quantified bycomparison with standard curves using samples comprising known amountsof the molecule of interest.

In some embodiments, the application provides a direct binding methodfor detecting an analyte of interest in a sample. In some embodiments ofthis method, molecules in the sample can be linked to a first carrier,for example, a magnetic bead. A binding partner of the analyte ofinterest can be linked to a second carrier, for example a polystyrenebead, which can comprise an ECL moiety. If a sample contains the analyteof interest, complexes comprising both the first carrier and the secondcarrier can form. The amount of ECL moiety associated with this complex,which is proportional to the amount of the biological material ofinterest in the sample, can be measured by techniques known in the art.In certain embodiments, the amount of the analyte of interest in asample can be quantified by comparison with standard curves usingsamples comprising known amounts of the molecule of interest.

Many variations on these types of binding assays are known to thoseskilled in the art and are compatible with the present methods.

There are many methods for quantifying the amount of ECL moiety present.The rate of energy input into the system can provide a measure of theECL moiety. Suitable measurements include, for example, measurements ofelectric current when the ECL moiety is excited electrochemically, therate of reductant or oxidant utilization when the ECL moiety is excitedchemically, or measurements of the absorption of electromagnetic energyin photoluminescent techniques. The ECL moiety can also be detected bymeasuring the emitted electromagnetic radiation. All of thesemeasurements can be made either as continuous, rate-based measurements,or as cumulative methods which accumulate the signal over a long periodof time. Rate-based measurements can be made using photomultipliertubes, photodiodes, or phototransistors that produce electric currentsproportional in magnitude to the incident light intensity. Cumulativemethods can involve the integration of rate-based data or the use ofphotographic film to directly provide cumulative data.

The application also provides for the isolation of a complex comprisingthe analyte of interest, at least one carrier, and an ECL moiety. Insome embodiments, a magnetic field can be used to separate the complex,e.g., when the at least one carrier is a magnetic bead. In someembodiments, separation of the complex can be achieved by precipitation,e.g., by the force of gravity when the mass of the complex is greaterthan the mass of the individual components. In some embodiments, afilter can be used to separate the complex from other components of thecomposition. The filter can, for example, have a pore size small enoughto retain the complex, but large enough to permit uncomplexed materialto pass through. In some embodiments, a size exclusion column can beused to separate the complex. Other properties that distinguish thecomplex from other components of the composition can also be used, forexample, hydrophobicity or affinity for other binding partners.

G. Diseases and Conditions

In certain embodiments, the analyte of interest can be a markerassociated with a disease or condition. The application thus provides amethod of detecting a marker associated with a disease or condition andthereby diagnosing a subject having a disease or condition. In someembodiments, the application provides a method to monitor theprogression of a disease or condition by monitoring the presence orquantity of a marker associated with a disease or condition. In someembodiments, the application provides a method for monitoring theeffectiveness of therapy used to treat a disease or condition bymonitoring the presence or quantity of a marker associated with adisease or condition.

The disease or condition can include an infectious disease caused by aninfectious agent, e.g., bacteria, fungi, parasites, viruses, or prions.Examples of bacterial pathogens include B. anthracis, E. coli, S.pneumoniae, S. pyogenes, S. bovis, S. agalactiae, S. aureus, S.epidermidis N. meningitidis, M. tuberculosis. Examples of viralinfections include smallpox, severe acute respiratory syndrome (SARS),human immuno-deficiency virus (HIV), Epstein-Barr virus (EBV), hepatitisB, hepatitis C, rhinovirus, influenza, respiratory syncytia virus (RSV),measles, polio, herpes simplex virus-1 (HSV-1) and herpes simplexvirus-2 (HSV-2). Examples of parasites include Plasmodium falciparum, P.vivax, P. malaria, Toxoplasma gondii. Trypanosoma cruzi, and Giardialamblia.

The disease can be cancer or an auto-immune disease. Markers associatedwith various cancers which can be analytes of interest, include mutantcyclin-dependent kinase 4 of melanoma; p17 protein of melanoma; gp 100of melanoma; melanoma associated antigen-1 (MART-1) (Melan-A) ofmelanoma (PCT publication WO94/21126); p15 protein of melanoma;tyrosinase of melanoma (PCT publication WO94/14459); melanoma associatedantigen (MAGE) 1, 2 and 3 of melanoma, thyroid medullary, small celllung cancer, colon and/or bronchial squamous cell cancer(PCT/US92/04354); melanoma associated antigen-Xp (MAGE-Xp) (U.S. Pat.No. 5,587,289); B melanoma antigen (BAGE) of bladder, melanoma, breast,and squamous-cell carcinoma (U.S. Pat. No. 5,571,711 and PCT publicationWO95/00159); G antigen (GAGE) (U.S. Pat. No. 5,610,013 and PCTpublication WO95/03422); renal tumor antigen (RAGE) family (U.S. Pat.No. 5,939,526); preferentially expressed antigen in melanoma (PRAME)(formerly DAGE; PCT publication WO96/10577); melanoma ubiquitous mutatedprotein (MUM-1/LB-33B) (U.S. Pat. No. 5,589,334); neuroblastomaamplified protein (NAG) (U.S. Pat. No. 5,821,122); FB5 (endosialin)(U.S. Pat. No. 6,217,868); PSMA (prostate-specific membrane antigen)(U.S. Pat. No. 5,935,818); gp75 of melanoma; oncofetal antigen ofmelanoma; carbohydrate/lipids such as mucin of breast, pancreas, andovarian cancer; GM2 and GD2 gangliosides of melanoma; oncogenes such asmutant p53 of carcinoma; mutant ras of colon cancer; erythroblasticleukemia viral oncogene homolog 2 (HER2/neu) proto-oncogene of breastcarcinoma; and viral products such as human papillomavirus proteins ofsquamous cell cancers of cervix and esophagus. Markers associated withautoimmune diseases include antibodies that specifically bind chromatinassociated with systemic lupus erythematosus, the presence of humanleukocyte antigen (HLA) allele DR2 (associated with multipleschlerosis), DR3 (associated with Graves disease) or DR4 associated withrheumatoid arthritis (Janeway et al. Immunobiology, Garland Publishing,New York 2001).

H. Kits

In certain embodiments, the application provides a kit for detecting ananalyte of interest in a sample. The kit can comprise a first carriercomprising at least one ECL moiety, a second carrier, at least onespecific binding partner of the analyte of interest linked to at leastone of the first and second carriers, at least one container, and,optionally, instructions. In certain embodiments the kit can comprise 2or more ECL moieties.

EXAMPLES

Chemicals and Materials: Tris(2,2′-bipyridyl)ruthenium(II)dichloridehexahydrate (Ru(bpy)₃Cl₂-6-H₂O), trifluoroacetic acid (TFAA, 99%),silver tetrafluoroborate (AgBF₄, 98%), and tri-n-propylamine (TPrA,99+%) obtained from Aldrich (Milwaukee, Wis.); lithiumtetrakis(pentafluorophenyl)borate (Li[(B(C₆F₅)₄)]-nEt₂O, n=2-3) obtainedfrom Boulder Scientific Co. (Mead, Colo.); tetrabutylammoniumtetrafluoroborate ((TBA)BF₄, electrochemical grade) obtained from Fluka(Milwaukee, Wis.); tris(hydroxymethyl)aminomethane (Tris, ultrapure)from Life Technologies (Rockville, Md.);1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC,SigmaUltra), N-hydroxysuccinimide (NHS), fluorescein biotin (90%),1-methylimidazole, and DNA hybridization buffer (PerfectHyb™ plus)obtained from Sigma (St. Louis, Mo.); sodium hydroxide (GR),hydrochloric acid (GR), sodium chloride (GR), ethyl ether (anhydrous),acetonitrile (HPLC), tetrahydrofuran (THF, GR), andethylenedinitrilotetraacetic acid (EDTA) obtained from EM (Gibbstown,N.J.); avidin (NeutrAvidin), D-biotin (ImmunoPure®), andbiotin-PEO-LC-amine obtained from Pierce (Rockford, Ill.); and methanol(spectroanalyzed grade) obtained from Fisher (Fairlawn, N.J.) were usedwithout further purification unless otherwise stated. Carboxylatepolystyrene microspheres/beads (PSB, 10 μm in diameter, 2.6% (w/w)aqueous suspension with 6.5×10⁴ beads/μL) and streptavidin coatedsuperparamagnetic polystyrene beads (referred to as magnetic beads orMB, (a) 1.0 μm in diameter, 10 mg/mL aqueous suspension with about9.5×10⁶ beads/μL; (b) 2.8 μm in diameter, 10 mg/mL aqueous suspensionwith about 6.5×10⁵ beads/μL) were purchased from PolySciences Inc.(Warington, Pa.) and Dynal Biotech Inc. (Lake Success, N.Y.),respectively. Synthetic 23-mer single-stranded DNA (ssDNA)oligonucleotides derived from the Bacillus anthacis (Ba813) wereobtained from Qiagen Operon (Alameda, Calif.) and had the followingsequences: (a) probe, 5′-[biotin-TEG]-AACGA TAGCT CCTAC ATTTG GAG-3′(p-ss-DNA, M.W.=7617 g/mol; SEQ ID NO: 1); (b) target or complementary,5′-[biotin-TEG]-CTCCA MTGT AGGAG CTATC GTT-3′ (t-ssDNA, M.W.=7608 g/mol;SEQ ID NO: 2); (c) non-complementary, 5′-[biotin-TEG]-TTAAC ACCTT AGCGACGGCT AGT-3′ (nc-ssDNA, MW=7593 g/mol; SEQ ID NO: 3); and (d) 2-basepairs mismatched oligomer sequence, 5′-[biotin-TEG]-CTCCA MCGT AGGAGTTATC GTT-3′ (2-bp-m-ssDNA; SEQ ID NO: 4), in which biotin-TEG containeda 16-atom mixed polarity spacer based on a triethylene glycol and usedto reduce the steric hindrance between the biotinylated DNA and surfaceconfined avidin/streptavidin interactions. Unless otherwise stated, allsolutions were freshly prepared with 18 M.OMEGA.-cm deionized Milli-Qwater (Millipore Corp., Bedford, Mass.)

ECL and Electrochemical Measurements. A three-electrode cell system wasused, with a 2.2 mm diameter Pt disk, 2.0 mm diameter Au or 3.0 mmdiameter glassy carbon (GC) disk as the working electrode, a Pt wire asthe counter electrode and a Ag/Ag+ (10 mM AgBF₄ and 50 mM TBABF₄ inMeCN) as the reference electrode. All electrodes were carefully cleanedbefore each experiment. The cleaning steps included: immersing theworking electrodes into a chromic acid solution, polishing with a 0.05μm alumina slurry (Buehler Ltd., Lake Bluff, Ill.), washing with copiousamounts of water, rinsing with MeCN, and replacing the porous Vycor tipand the glass tube for the reference electrode. A 5 mL disposable glassvial served as the electrochemical cell. To exclude the possibility ofthe ECL signal being generated from a Ru(bpy)₃ ²⁺ contaminated system,virgin glassware and electrodes were used whenever necessary. The ECLintensities, along with the cyclic voltammograms (CV), were measuredsimultaneously with a home-built potentiostat combined with aphotomultiplier tube (PMT, Hamamatsu R4220p, Japan) installed under theelectrochemical cell. A voltage of −750 V was supplied to the PMT with ahigh-voltage power supply (Bertan High Voltage Corp., Series 225,Hicksville, N.Y.).

All measurements were conducted at a temperature of 20±2° C., unlessotherwise stated.

Example 1 Synthesis of Ru(bpy)₃ ²⁺ Containing ECL Labels

Tris(2,2′-bipyridyl)ruthenium(II) tetrakis(pentafluorophenyl)borate(Ru(bpy)₃[B(C₆F₅)₄]₂) was used as the ECL label in the present study,because, as shown in the next sections, this complex can be effectivelyloaded into polystyrene beads using a suitable organic solution andmaintained entrapped within the beads during a series of modification ofthe beads in aqueous solutions. In other words, Ru(bpy)₃[B(C₆F₅)₄]₂ issufficiently soluble in organic solvents but completely insoluble inaqueous solutions. Another reason to choose Ru(bpy)₃[B(C₆F₅)₄]₂ as theECL label was the fact that the Ru(bpy)₃ ²⁺ moiety of the complex has avery high ECL efficiency. Ru(bpy)₃[B(C₆F₅)₄]₂ was prepared by ametathesis reaction between Ru(bpy)₃Cl₂ and Li[B(C₆F₅)₄]-nEt₂O (n=2-3)in water. The precipitate was washed with water, recrystallized from anacetonitrile/water solution, and dried under vacuum.

Example 2 Electrochemical and ECL Behavior of Ru(bpy)₃ ²⁺ in MeCN UsingTPrA as a Coreactant

The cyclic voltammetric and ECL responses of 0.10 μM Ru(bpy)₃[B(C₆F₅)₄]₂in MeCN containing 0.10 M (TBA)BF₄ electrolyte-0.10 M TPrA coreactant ata Pt electrode at a scan rate of 50 mWs are shown in FIG. 4. TPrA startsto oxidize at potentials around 0.5 V vs Ag/Ag⁺, and shows a maximumoxidation peak at about 0.75 V vs Ag/Ag⁺ (FIG. 4 a). When the electrodeis scanned to a potential more positive than 1.1 V vs Ag/Ag⁺ where theRu(bpy)₃ ²⁺ is oxidized to Ru(bpy)³⁺ Ru(bpy)³⁺ (FIG. 4 c), the ECL isproduced (FIG. 4 b). The ECL intensity continuously increases withincreasing potential, finally forming a broad peak with a half-wavewidth of about 700 mV and a peak potential at about 1.6 V vs Ag/Ag⁺. Onthe reverse scan, a larger ECL intensity and similar peak position isobserved. Note that the oxidation potential of Ru(bpy)₃ ²⁺ can slightlyshift positive in the presence of TPrA, since the ECL peak potentialsare more positive in comparison with the oxidation potential of Ru(bpy)₃²⁺ in the absence of TPrA (FIGS. 4 b and c). As expected, a change inthe counter ions of Ru(bpy)₃ ²⁺ complexes, e.g., from B(C₆F₅)₄ ⁻ to ClO₄⁼, did not change the ECL behavior. In contrast to the case in aqueoussolution, where a pre-wave ECL appeared in the potential region of TPrAoxidation due to the formation of excited state Ru(bpy)₃ ²⁺* on reactionof TPrA*⁺ with Ru(bpy)₃ ⁺ (formed by reaction of Ru(bpy)₃ ²⁺ with TPrA*)when a μM level of Ru(bpy)₃ ²⁺ was used, (Miao, Choi and Bard, 2002, J.Am. Chem. Soc. 124:14478) no noticeable corresponding ECL signal wasfound in MeCN. This suggests that under the present experimentalconditions, either the life time of TPrA*⁺ in MeCN is shorter than inneutral aqueous solutions, or TPrA*⁺ is not energetically powerfulenough to oxidize Ru(bpy)₃ ⁺ to Ru(bpy)₃ ²⁺*. Apart from this, weconclude that the ECL mechanism developed in aqueous solutions usingTPrA as a coreactant is operative in MeCN.

The ECL intensity as a function of TPrA concentration is shown in FIG. 5a, where the highest ECL intensity region corresponds to a TPrAconcentration of 30 mM. As would be expected, on the basis of the ECL-pHdependence study in aqueous solution, (Leland et al. 1990, J.Electrochem. Soc. 137:3127) by adding trifluoroacetic acid (TFAA) into aRu(bpy)₃ ²⁺/TPrA/MeCN solution, hence changing the acidity of thesolution, the ECL intensity is changed (FIG. 5 b). A combination of 100mM TPrA with 55 mM TFAA gave the largest ECL response.

The ECL intensity and stability were also affected by the electrodematerial used. Pt and Au electrodes showed similar responses; the ECLwas stable over several potential cycles, with a slightly smallerphotocurrent density found at a Pt compared to an Au electrode. At a GCelectrode, however, only the forward scan of the first potential cycleproduced light. After polishing of the GC electrode, the light aroseagain, suggesting the electrode surface had been blocked by a film ofsome kind. The relative ECL intensity, obtained from a MeCN solutioncontaining 0.10 μM Ru(bpy)₃[B(C₆F₅)₄]₂-0.10 M TPrA-0.055 M TFM-0.10 M(TBA)BF₄ during the first potential cycle between 0 and 3.0 V vs Ag/Ag+at a scan rate of 50 mV/s, at Au, Pt and GC electrode had a ratio of100:93:61.

Interestingly, even in the absence of Ru(bpy)₃ ²⁺, a TPrA inacetonitrile solution with 0.10 M (TBA)BF₄ can also produce an ECLsignal (FIG. 6 a). Purification of the TPrA and MeCN by distillation,changing the electrolyte from (TBA)BF₄ to (TBA)ClO₄ or using a newlyopened electrochemical grade electrolyte, using virgin glassware andelectrodes, and covering the Pt counter electrode with a glass tubecoated with or without a layer of black plastic, did not change theresult. The ECL had a peak potential value of 2.1 V vs Ag/Ag⁺, which isa 500 mV shift compared to that obtained in the presence of 0.10 μMRu(bpy)₃ ²⁺ (FIG. 4 b). As shown previously in FIG. 5 a, in the absenceof TPrA, a Ru(bpy)₃ ²⁺ in MeCN solution with 0.10 M (TBA)BF₄ did notgive an observable ECL response on the same intensity scale with a scanonly to positive potentials. Thus, the ECL signals shown in FIG. 6 amust originate from TPrA, and are probably due to the charge-transferreaction inverse photoemission (CTRIP) associated with TPrA* freeradicals (Murakoshi et al. 1992, J. Phys. Chem. 96:4593; Uosaki et al.1991, J. Phys. Chem. 95:779; Uosaki et al. 1990, Chem. Lett. 7; 1159;McIntyre et al. 1987, J. Electroanal. Chem. Interfac. Electrochem.228:293; McIntyre et al. 1986, Phys Rev Lett. 56:651; McIntyre et al.1985, J. Electroanal. Chem. Interfac. Electrochem 196:199; Murakoshi etal. 1993, Conden Mar Mater. Phys. 47:2278; Ouyang and Bard 1988, J.Phys. Chem. 92:5201; Ouyang and Bard 1987, J. Phys. Chem. 91:4058). Theintegrated ECL intensity obtained from FIG. 6 a, which is about 12% ofthat obtained from FIG. 4 b, is significant, since in the absence ofTPrA, the residual photocurrent measured from a 0.10 M (TBA)BF₄/MeCNsolution is significantly less (FIG. 6 d). The background TPrA-relatedECL signals was suppressed dramatically by adding TFAA to the solution(FIG. 6 b), and a further elimination of the “unwanted” signals wasachieved by a addition of 1% (v/v) H₂O into the 0.10 M TPrA-0.055 MTFM-0.10 M (TBA)BF₄ MeCN solution (FIG. 6 c). FIG. 6 e displays therelative ECL intensities obtained from FIGS. 6 a to 6 d.

Example 3 Loading ECL Labels into Polystyrene Beads

Carboxylate polystyrene beads having a 10 μm diameter were separatedfrom an appropriate volume (0.10-1.0 mL) of 2.6% (w/w) polystyrene beadssuspension with an Eppendorf 5415D centrifuge (Brinkmann Instruments,Inc. Westbury, N.Y.) at 10 k rpm for 5 minutes, and then washed oncewith 1 mL of water.

The beads were dried under vacuum at 60° C. for 1 hour, followed byadding 1.5 mL of the ECL label Ru(bpy)₃[B(C₆F₅)₄]₂-saturated (0.7 mM) 5%THF-95% MeOH (v/v) solution into a 2 mL microcentrifuge tube containingthe PSB. The mixture was rotated with a Dynal™ sample mixer (DynalBiotech Inc.) at 20 rpm for 2 hours, followed by centrifugation andwashing with 50% MeOH-50% H₂O (v/v) twice. The resulting ECLlabel-containing yellowish polystyrene beads, designated as Ru(II)<PSB,were further dried under vacuum at 60° C. for 1 hour. During the courseof the above treatments, the polystyrene beads were first swelled in theECL label containing 5% THF-95% MeOH organic solution, allowing thewater-insoluble ECL labels to diffuse into the polymer matrix, wherethey were entrapped when the organic solvents were removed from thebeads by vacuum evaporation. The effective loading of the ECL labelsinto the polystyrene beads can be visually verified via the fluorescentimage (FIG. 2 a) taken with a Nikon Eclipse TE 300 inverted microscope(Nikon Instruments Inc., Melville, N.Y.) coupled with a Magnafire-Model599806 Olympus America CCD camera (Olympus America, Melville, N.Y.). Atypical loading capacity of 7.5×10⁹ Ru(bpy)₃[B(C₆F₅)₄]₂ molecules perbead was estimated on the basis of the ECL data obtained from Ru(II)<PSBdissolved in MeCN and a standard Ru(bpy)₃[B(C₆F₅)₄]₂ solution using TPrAas a coreactant.

Example 4 Immobilizing Avidin on the Surface of Ru(II)<PSB

A layer of avidin was covalently attached to the surface of Ru(II)<PSBvia the formation of Ru(II)<PSB—CO—NH-avidin, by immersing the beadsinto 1.5 mL of freshly prepared 25 μM avidin in 0.10 M 1-methylimidazolebuffer (pH 7) containing 0.10 M EDAC and 0.10 M NHS, and rotating themixture at about 40 rpm for 1 h. The newly formed avidin coatedRu(II)<PSB, designated as Ru(II)<PSB/Avidin, were centrifuged from thereaction solution at 5-10 k rpm for 5 min, and washed with 1 mL of“1×B&W buffer” (1× buffer & wash solution, 5 mM Tris-HCl (pH 7.5)+0.5 mMEDTA+1.0 M NaCl) three times. The final Ru(II)<PSB/Avidin product wasre-suspended in 1×B&W buffer solution that had the same volume as thestarting PSB suspension (0.10-1.0 mL) and kept at about 4° C. until use.Approximately, 6.5×10⁴ Ru(II)<PSB/Avidin beads/μL can thus be estimated,with a assumption of no loss of the beads during the preparation ofRu(II)<PSB/Avidin. FIG. 2 b shows a bright green fluorescent image ofRu(II)<PSB/Avidin after the beads reacted with fluorescein biotin,suggesting that a high quality layer of avidin was formed on the surfaceof Ru(II)<PSB. In contrast, non-specifically adsorbed fluorescein biotinon “bare” Ru(II)<PSB only generate a very weak fluorescent image. Thebinding capacity of Ru(II)<PSB/Avidin for a biotinylated 23-mer ssDNA(p-ssDNA) was found to have a value of 0.565 nmoles (p-ssDNA)/mg PSB or1.4×10⁸ p-ssDNA molecules/bead, on the basis of fluorescein biotintitration experiments (see FIG. 10 and Table 1, below).

Example 5 Attaching ssDNA to the Surface of MB and Ru(II)<PSB/AvidinBeads

Probe DNA-MB conjugates. Streptavidin coated magnetic beads (MB), havingeither a 1.0 μm or a 2.8 μm diameter, were used as the probe DNAcarrier. To form probe DNA-MB conjugates, 5.0 μL, of 1.0 μm MB, or 10.0μL, of 2.8 μm MB, was first transferred into a 2 mL microcentrifugetube, then separated from the original suspension with a magnet (DynalMPC®-S), followed by washing once with 200 μL, of “2×B&W buffer” (buffer& wash solution: 10 mM Tris-HCl (pH 7.5), 1.0 mM EDTA, 2.0 M NaCl) andtwice with 200 μL, of 1×B&W buffer before immersing the beads into 100μL, of 2.5 μM biotinylated p-ssDNA and incubating for 30 to 60 minuteswith gentle rotation at 40 rpm. The probe DNA-MB conjugates formed weresubsequently separated and washed with 200 μL, of 1×B&W buffer threetimes, transferred to a new 2 mL microcentrifuge tube to avoid possibleprobe DNA adsorption on the wall of the previous tube, and resuspendedin 20 μL, hybridization buffer. The conjugates produced in this way hada saturated probe DNA coverage of about 2.53 and 1.11 nmoles(p-ssDNA)/mg (beads), or 1.6×10⁶ and 1.0×10⁷ p-ssDNA molecules per bead,for 1.0 μm and 2.8 μm diameter MB, respectively (see FIG. 10 and Table1).

TABLE 1 Binding Capacity p-ssDNA p-ssDNA Type of nmoles per moleculesBeads mg Beads per Bead Turning Point  10 μm PSB 0.565 1.4 × 10⁸ 20 μLPSB~29.4 μL of 10 μM p-ssDNA 1.0 μm MB 2.53 1.6 × 10⁶ 10 μL MB~25.3 μLof 10 μL p-ssDNA 2.8 μm MB 1.11 1.0 × 10⁷ 20 μL MB~22.2 μL of 10 μMp-ssDNA

Target DNA-Ru(II)<PSB/Avidin conjugates. 100 μL of an appropriateconcentration of biotinylated t-ssDNA (1.0×10⁻⁸ to 1.0×10⁻¹⁵ M), or1.0×10⁻⁹ M non-complementary-ssDNA (nc-ssDNA) and 2 base pairmismatched-ssDNA (2-bp-m-ssDNA), was added to 25 μL of about 6.5×10⁴beads/μL Ru(II)<PSB/Avidin in 1×B&W buffer and incubated for 1 hour withgentle mixing at a rotation rate of 20 rpm, washed twice with 200 μL of1×B&W buffer, centrifuged at 3 k-5 k-10 k rpm for 5 min, and resuspendedin 50 μL of the hybridization buffer.

Example 6 DNA Hybridization and ECL Detection

The newly prepared target DNA-Ru(II)<PSB/Avidin conjugates (Example 5)were transferred into 2 mL centrifuge tubes containing previously formedprobe DNA-MB conjugates (Example 5). An appropriate volume of thehybridization buffer was added into the tubes to make a totalhybridization solution volume of 200 μL. After gentle mixing at 20 rpmfor 1 hour, the probe DNA-MB target DNA-Ru(II)<PSB/Avidin aggregateswere magnetically separated from the “solution” containing free unboundRu(II)<PSB/Avidin beads, washed gently with 200 μL of 1×B&W buffer threetimes, and carefully transferred into a new centrifuge tube to minimizethe possible adsorption of free Ru(11)<PSB/Avidin beads on the wall ofthe tube. This kind of nonspecific adsorption can produce asignificantly high level of background ECL, since, along with the DNAhybridization aggregates, free Ru(II)<PSB/Avidin beads on the wall canalso be dissolved in MeCN. The aggregates were finally washed with 200μL of water, and dissolved in a 0.50 mL of 0.10 M TPrA-0.055 M TFAA-0.10M (TBA)BF₄ MeCN solution for the later ECL measurements. The formationof probe DNA-MB←→target DNA—Ru(II)<PSB/Avidin aggregates after DNAhybridization can be clearly verified via a SEM image shown in FIG. 3,in which both the probe DNA and the complementary DNA had aconcentration of 5 μM, the initial ratio of MB/PSB=29, and the size ofthe MB and the PSB was 1.0 μm and 10 μm, respectively.

A linear relationship between the ECL intensity and theRu(bpy)₃[B(C₆F₅)₄]₂ concentration in a range of 0.10 nM to 1.0 μM wasfound in 0.10 M TPrA-0.055 M TFAA-0.10 (TBA)BF₄ MeCN with the additionof 1% water (FIG. 7 a). Under the same experimental conditions, a goodcorrelation between the ECL intensity and the number of 10 μm diameterpolystyrene beads loaded with Ru(bpy)₃[B(C₆F₅)₄]₂ was also observed(FIG. 7 b). The beads were dissolved in a 0.50 mL of electrolytesolution, to demonstrate that the polystyrene did not produce or affectthe ECL signal. By comparing FIG. 7 b with 7 a, it is clear that thelight intensity generated from 20 Ru(bpy)₃ ²⁺ loaded beads is equivalentto that from 0.5 nM Ru(bpy)₃ ²⁺. The loading capacity of the beads wasthus determined to be 7.5×10⁹ Ru(bpy)₃[B(C₆F₅)₄]₂ molecules per bead.This result is consistent with the data obtained on the basis of the“bulk beads” ECL measurement.

Two sets of experiments were designed for the ECL detection of DNAhybridization. In the first, 1.0 μm diameter MB with a ratio of MB toPSB beads of 29 was used. As shown in FIG. 8 a, in this case, the ECLintensity was proportional to the target DNA concentration over a rangeof 10 μM to 10 nM, and the two-base mismatched 2-bp-m-ssDNA andnoncomplementary nc-ssDNA can be readily distinguished from thecomplementary DNA hybridization. Note that unlike the examples shown inFIG. 7, no water was added to the electrolyte solution because the newlyformed MB-PSB conjugates and the microcentrifuge tube already containedsufficient water. Note also that no background subtraction was made forthe ECL intensity shown in FIG. 8. By reducing the ratio of MB to PSB,and hence increasing the amplification factor of Ru(bpy)₃ ²⁺ to t-ssDNA,DNA hybridizations at much lower concentrations of target DNA should bedetectable. As demonstrated infra, statistically, one 10 μm diameter PSBcan be pulled out with one 2.8 μm diameter MB. As a result, ECL signalsrelated to the DNA hybridization occurred at a very low target DNAconcentration and thus can be detectable when the 2.8 μm MB and 10 μmPSB is present at a low ratio. FIG. 8 b shows the results of such anexample, in which the ratio of 2.8 μm MB/10 μm PSB=4. The t-ssDNA can bedetected at a concentration as low as 1.0 fmol. Even under theseconditions, the obtained ECL intensity is larger than, and thusdistinguishable from, that obtained from the DNA hybridization of2-bp-m-ssDNA and nc-ssDNA when 1.0 nM of each species was used.

Example 7

Attaching Biotin-PEO-LC-Amine to Carboxylate Polystyrene Beads and thePoisson Distribution Test

Biotin-PEO-LC-amine (M.W.=418.6 g/mol) is a water soluble cross-linkerwith a 22.9.ANG. polyethylene oxide (PEO) based spacer arm used toreduce the steric hindrance of biotin and avidin interactions (2003-2004Applications Handbook & Catalog, Pierce Biotechnology, Inc. 2003).Biotin-PEO-LC-amine molecules were covalently attached to the surface ofcarboxylate polystyrene beads via the formation of amide bond betweenthe primary amine group of the cross-linker and the carboxyl group ofthe beads in the presence of 0.10 M EDAC-0.10 M NHS in 0.10 M1-methylimidazole buffer (pH 7). One mL of 5 mM biotin-PEO-LC-amine wasused to react with the PSB, separated from 250 μL of 2.6% PSBsuspension. The reaction was carried out for 2 hours with a rotationrate of 40 rpm. The cross-linker modified PSB, designated asPSB—CO—NH-LC-PEO-biotin, was subsequently separated and washed with 400μL of 1×B&W buffer 3 times, re-suspended in 250 μL of 1×B&W buffer, andthen kept at 4° C. until use.

Poisson distribution measurements were performed using 10 μm diameterPSB—CO—NH-LC-PEO-biotin beads, with two different sizes ofstreptavidin/polystyrene coated magnetic beads (1.0 and 2.8 μm indiameter Dynal™ beads). When tens of thousands ofPSB—CO—NH-LC-PEO-biotin beads are mixed sufficiently in solution, withthe same, or a larger number, of either 1.0 or 2.8 μm magnetic beads,the probability that the PSB—CO—NH-LC-PEO-biotin beads will stick, viathe irreversible reaction between the biotin of the PSB and thestreptavidin of the MB, can be observed and compared to that predictedfor a Poisson distribution. Experimentally, 50 μL of about 6.5×10⁴beads/pL PSB—CO—NH-LC-PEO-biotin beads (3.3×10⁶ PSB in total) werediluted with 175 μL of 1×B&W buffer, and transferred to a 2.0 mLmicrocentrifuge tube containing a known number of streptavidin coatedmagnetic beads (1.0 μm in diameter) that had been separated magneticallyfrom the manufacturer's original suspension and washed once with 200 μLof 2×B&W buffer. The mixture was immediately shaken and rotated at 40rpm for 1 hour before the PSB-MB aggregates were magnetically separatedfrom the mixture. The resulting supernatant contained unbound freePSB—CO—NH-LC-PEO-biotin beads, and the number of PSB in the supernatantwas determined by optical examination with an inverted microscope.Similar procedures were used to study the Poisson distribution of 2.8 μmMB. However, in this case, only half the amount of thePSB—CO—NH-LC-PEO-biotin beads, i.e., 1.6×10⁶ beads, were used to reactwith a known amount of MB.

When a very large number of magnetic beads and polystyrene beads aremixed together, the probability P(m, n) that these two kinds of beadscollide and react irreversibly should follow a Poisson distribution anddepend on the following two parameters: (a) the initial ratio ofmagnetic beads to polystyrene beads m, and (b) the number of magneticbeads bound to each polystyrene bead n. For example, if an equal numberof MB and PS beads were mixed (m=1), the average number of MB bound toPS should be one. However there will be a distribution, with n=0, 1, 2 .. . to lead to this average value. The relationship between P(m, n), m,and n can be described by the Poisson distribution as follows:P(m,n)=e^(−m)[m^(−n)/n!] n=0, 1, 2, . . . (See, Haight, Handbook of thePoisson Distribution; John Willey & Sons, Inc.: New York, 1967.)

Table 2 lists the P(m,n) values for different values of m and n. Withthis table and the Poisson distribution test data (provided above), onecan estimate the minimum number of magnetic beads required to bind andpull out one single polystyrene bead from the reaction solution. Forexample, from the number of PSB collected from the supernatant, thepercentage of the PSB bound with MB and pulled out magnetically from thereaction mixture can be calculated. A set of “bound PSB %” data with anumber of known m values, e.g., m=1, 2, 3, 4, 5 . . . , can then beobtained experimentally. If the data fit the theoretical values of P(m,n>j) (Table 2), where m is known from the experiments conducted, j=0, 1,2, 3 . . . , and

${{P\left( \; {m,{n > j}} \right)} = {\overset{\sim}{\sum\limits_{i = {j + 1}}}{P\left( {m,i} \right)}}},$

then the minimum number of magnetic beads required to bind and pull outone single polystyrene bead must be j+1.

TABLE 2 m n 1 2 3 4 5 6 8 10 12 0 0.36788 0.13534 0.049787 0.0183160.0024788 4.5400e−05 6.1442e−06 1 0.36788 0.27067 0.14936 0.0732630.033690 0.014873 0.0026837 7.3731e−05 2 0.18394 0.27067 0.22404 0.146530.084224 0.044618 0.010735 0.0022700 0.00044238 3 0.061313 0.180450.22404 0.19537 0.14037 0.089235 0.028626 0.0075667 0.0017695 4 0.0153280.090224 0.16803 0.19537 0.17547 0.13385 0.057252 0.018917 0.0053086 50.036089 0.10082 0.15629 0.17547 0.16062 0.091604 0.037833 0.012741 . .. . . . . . . . . . . . . . . . . . . . . . . . . Sum 1 1 1 1 1 1 1 1 1

FIG. 9 shows two examples of such a test. In the first example (FIG. 9a), 2.8 μm MB and 10 μm PSB were used, and a minimum binding ratio ofMB/PSB=1 can be deduced. In the second example (FIG. 9 b), instead of2.8 μm MB, 1.0 μm MB was used to react with 10 μm PSB. In this case ahigher minimum MB to PSB binding ratio of 3 was obtained. These bindingratios can be utilized to optimize experimental conditions for the DNAhybridization between MB and PSB, so that a minimum target DNAconcentration could be detected.

Example 8 Loading of Two Aromatic Hydrocarbons, DPA and Rubrene, intoPolystyrene Bead

In addition to Ru(bpy)₃[B(C₆F₅)₄]₂, aromatic hydrocarbons, e.g.,9,10-diphenylanthracene (DPA, FIG. 11 a) and rubrene (RUB, FIG. 11 b),were also loaded into polystyrene beads (PSB). As a result, ECL labelswith different emission wavelengths were obtained. The loadingprocedures were similar to those used for Ru(bpy)₃[B(C₆F₅)₄]₂entrapping, except that 5% THF-95% MeOH “swelling solvent” was replaceby 5% benzene-95% MeOH so that the two aromatic hydrocarbons aresufficiently soluble in benzene contained solvent. FIG. 12 summarizesthe loading procedures.

The entrapping of DPA and RUB into PSB was visually verified usingfluorescent imaging with UV light excitations. As shown in FIGS. 13 aand b, strong blue and yellow to orange fluorescent images are observedfor DPA and RUB loaded PSB, respectively. In contrast, PSB with noaromatic hydrocarbon showed weak green fluorescence (FIG. 13 c).

A loading capacity of 7.5×10⁹ DPA molecules per bead or 4.0×10⁸ RUBmolecules per bead was estimated on the basis of the ECL data obtainedfrom the DPA or RUB loaded PSB dissolved in MeCN and a standard DPA orRUB solution using tri-propylamine (TPrA) as a coreactant. FIG. 14 showsthe CV and ECL behavior of (a) DPA loaded PSB dissolved in MeCN and (b)0.25 mM DPA acetonitrile solution using TPrA as a coreactant. The CV andECL behavior of RUB loaded PSB dissolved in MeCN and 35 μM RUBacetonitrile solution using TPrA as a coreactant is shown in FIGS. 15 aand 15 b, respectively.

Example 9 ECL Detection of C Reactive Protein (CRP)

Ru(II)<PSB/Avidin←Anti-CRP conjugates were prepared as follows:0.100-0.500 mL of Ru(II)<PSB/Avidin (6.5×10⁴ beads/μL) (see Example 4)were mixed with 1 mL of 2.0 mg/mL biotinylated anti-CRP (Miao and Bard,2003, Anal. Chem. 75:5825) in 0.10 M PBS buffer (0.1 M sodium phosphate,0.15 M sodium chloride) (pH 7.2) (Pierce, Rockford, Ill.) with arotation rate of 25 rpm at room temperature for 1 hour. The newly formedconjugates were collected by centrifugation, washed with 1×B&W bufferthree times (see Example 4), and resuspended in 1 mL of 2% bovine serumalbumin (BSA)/0.10 M PBS (pH 7.2) solution for 30 minutes. Aftercentrifugation and washing (as above), the conjugates were suspended ina suitable volume (0.100-0.500 mL) of 0.10 M PBS (pH 7.2) buffersolution and kept at 4° C. until use.

MB←Anti-CRP conjugates were prepared as follows: 0.100-0.500 mL of 2.8μm diameter streptavidin-coated magnetic beads (MB, 6.5×10⁵ beads/μL)were magnetically separated and washed once with 1 mL of 2×B&W bufferand twice with 1 mL of 1×B&W buffer, followed by mixing with 1.5 mL of2.0 mg/mL biotinylated anti-CRP in 0.10 M PBS buffer (pH 7.2) at arotation rate of 25 rpm at room temperature for 1 hour. The newly formedMB←anti-CRP conjugates were washed with 1 mL of 1×B&W buffer 3 times,resuspended in a suitable volume (0.100-0.500 mL) of 0.10 M PBS (pH 7.2)buffer solution, and stored at 4° C. until use.

Sandwich-Type Ru(II)<PSB/Avidin←Anti-CRP<CRP>MB←Anti-CRP conjugates wereformed as follows: 20 μL of Ru(II)<PSB/Avidin←Anti-CRP Conjugates(1.3×10⁶ PSB in total) and 20 μL of MB Anti-CRP Conjugates (1.3×10⁷ MBin total) were gently mixed with a CRP sample in 200 μL of 0.10 M PBS(pH 7.2) buffer solution at room temperature for 2 hours. Thesandwich-type conjugates were magnetically separated from the mixturesolution and washed 3 times with 200 μL of 1×B&W buffer. The conjugateswere then transferred, with a small volume of PBS buffer, to a new 2 mLcentrifuge tube, so that possible adsorption of freeRu(II)<PSB/Avidin←Anti-CRP on the wall of the old tube was minimized(cf. Example 6). Finally, the “magnetic conjugates” were separated fromthe solution with a magnet.

CRP was detected by ECL. The obtained sandwich-type conjugates weredissolved in 0.500 mL of 0.10 M TPrA-0.055 TFAA-0.10 M (TBA)BF₄ MeCNsolution, and the ECL experiments were carried out at a 2.2 mm diameterPt electrode using cyclic voltammetry with a scanning potential windowbetween 0 and 2.8 V vs. Ag/Ag⁺ (10 mM AgBF₄ in 0.10 M (TBA)BF₄ MeCN) ata scan rate of 50 mV/s. As expected, the profiles of CV and ECL obtainedfrom the sandwich-type conjugates were very similar to those shown inFIGS. 4 a and c, since, in both cases, the “reactive species”, Ru(bpy)₃²⁺ and TPrA, were the same. As shown in FIG. 16, the ECL intensity (theaverage of the forward scan peak intensity and the reverse scan peakintensity) is linearly proportional to the CRP concentration over therange of 0.010-10 μg/mL.

All references cited herein are incorporated herein by reference intheir entirety. To the extent publications and patents or patentapplications incorporated by reference contradict the disclosurecontained in the specification, the specification is intended tosupersede and/or take precedence over any such contradictory material.

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe specification and attached claims are approximations that can varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches.

Many modifications and variations of the present methods andcompositions can be made without departing from their spirit and scope,as will be apparent to those skilled in the art. The specificembodiments described herein are offered by way of example only and arenot meant to be limiting in any way. It is intended that thespecification and examples be considered as exemplary only.

1. A method of detecting an analyte of interest in a sample, comprising(a) forming a composition comprising: (A)_(k), (B)_(u), (C), (D)_(x)wherein A is an ECL moiety which can be induced to repeatedly emitelectromagnetic radiation by direct exposure to an electrochemicalenergy source; and the ECL moiety is soluble in organic solvent andinsoluble in aqueous solvent; B is a first carrier comprising aplurality of the ECL moieties entrapped within its interior; and B iseither linked to the analyte of interest or linked to a first specificbinding partner of the analyte of interest; C is the sample which maycontain the analyte of interest; and D is a second carrier which iseither linked to the analyte of interest or linked to a second specificbinding partner of the analyte of interest; wherein k, u, and x are eachan integer equal to or greater than 1; the first and second carriers arenot both linked to the analyte of interest; (b) separating a complexcomprising A, B, D and the analyte of interest from other components ofthe composition; (c) inducing the ECL moieties from the complex torepeatedly emit electromagnetic radiation by directly exposing themoiety to electrochemical energy; and (d) detecting the emittedelectromagnetic radiation and thereby detecting the presence of theanalyte of interest.
 2. The method of claim 1, wherein B is linked tothe first specific binding partner; and D is linked to the secondspecific binding partner.
 3. The method of claim 1, wherein the analyteof interest is a protein; the first specific binding partner is anantibody, a part of an antibody, or a binding protein; and the secondspecific binding partner is an antibody, a part of an antibody, or abinding protein.
 4. The method of claim 1, wherein the analyte ofinterest is a nucleic acid; the first specific binding partner is anucleic acid; and the second specific binding partner is a nucleic acid.5. The method of claim 1, wherein the first carrier is a syntheticorganic polymer bead.
 6. The method of claim 5, wherein the firstcarrier is a polystyrene bead and the second carrier is a magnetizablebead.
 7. The method of claim 5, wherein the synthetic organic polymerbead comprises a compound chosen from polystyrene, polyacrylic, vinylpolymers, acrylate, nylon, polymethacrylate, polyacrylamide,polyacrylonitrile, PVDF, poly(lactide-co-ethylene glycol), andpolyolefins.
 8. The method of claim 1, further comprising the additionof an ECL coreactant to the composition.
 9. The method of claim 8,wherein the coreactant is an amine or an amine moiety.
 10. The method ofclaim 1, wherein the ECL moiety comprises a metal ion selected fromosmium or ruthenium.
 11. The method of claim 1, wherein the ECL moietycomprises bis(2,2′-bipyridyl)-ruthenium(II) ortris(2,2′-bipyridyl)ruthenium(II).
 12. The method of claim 1, whereinsaid method further comprises the addition of an amine ECL coreactant tothe composition; the analyte of interest is a protein; the firstspecific binding partner is an antibody, a part of an antibody, or abinding protein; and the second specific binding partner is an antibody,a part of an antibody, or a binding protein; first carrier is asynthetic organic polymer bead; and the ECL moiety comprises a metal ionselected from osmium or ruthenium and three bidentate ligands.
 13. Themethod of claim 12, wherein the first carrier is a polystyrene bead; thesecond carrier is a magnetizable bead; amine ECL coreactant comprisestripropylamine; and the ECL moiety comprisesbis(2,2′-bipyridyl)-ruthenium(II) or tris(2,2′-bipyridyl)ruthenium(II).14. The method of claim 1, further comprising the step of dissolving Bin an organic solvent.
 15. A composition for use in detecting an analyteof interest comprising: a synthetic organic polymer bead comprising aplurality of ECL moieties entrapped within its interior, wherein thesynthetic organic polymer bead is either linked to the analyte ofinterest or linked to a specific binding partner of the analyte ofinterest; wherein the ECL moieties can be induced to repeatedly emitelectromagnetic radiation by direct exposure to an electrochemicalenergy source; and the ECL moieties are soluble in an organic solventand insoluble in an aqueous solvent.
 16. The composition of claim 15,wherein the ECL moieties comprise ruthenium and three bidentate ligands.17. The composition of claim 15, wherein the ECL moieties comprisebis(2,2′-bipyridyl)ruthenium(II) or tris(2,2′-bipyridyl)ruthenium(II).18. The composition of claim 15, wherein the ECL moieties compriseRu(bpy)₃[B(C₆F₅)₄]₂.
 19. A composition for detecting an analyte ofinterest in a sample comprising: (A)k) (B)₁₁, (C), (D)_(x) wherein A isan ECL moiety which can be induced to repeatedly emit electromagneticradiation by direct exposure to an electrochemical energy source; andthe ECL moiety is soluble in organic solvent and insoluble in aqueoussolvent; B is a first carrier comprising a plurality of the ECL moietiesentrapped within its interior; and B is either linked to the analyte ofinterest or linked to a first specific binding partner of the analyte ofinterest; C is the sample which may contain the analyte of interest; andD is a second carrier is either linked to the analyte of interest orlinked to a second specific binding partner of the analyte of interest;wherein k, u, and x are each an integer equal to or greater than 1; andthe first and second carriers are not both linked to the analyte ofinterest.
 20. A kit for detecting an analyte of interest in a samplecomprising: at least one first carrier comprising a plurality of ECLmoieties entrapped within its interior; wherein the first carrier iseither linked to the analyte of interest or linked to a first specificbinding partner of the analyte of interest; at least one second carrier,which is either linked to the analyte of interest or linked to a secondspecific binding partner of the analyte of interest; provided that thefirst carrier and the second carrier are not both linked to the analyteof interest; wherein the ECL moieties can be induced to repeatedly emitelectromagnetic radiation by direct exposure to an electrochemicalenergy source; and the ECL moieties are soluble in organic solvent andinsoluble in aqueous solvent.